Introduction
Sometimes invoices or other records in Wello may not sync to SAP and get stuck in the “Ready for ERP” status. This article explains the most common reasons why this happens, what each error means, and the exact steps you can take to fix it
(Example of the Error Seen in Logs)
This can happen for a few different reasons, and most of the time it is related to SAP not responding properly when Wello tries to send the data.
This article explains, in plain language,
Why the sync may fail,
What usually causes it, and
What you can do to fix it.
A. Common Reasons and Solutions
Below are the most common and practical reasons we see
1. SAP Service Layer Not Stable
Cause: SAP’s Service Layer may be slow, overloaded, or temporarily down.
What you’ll see: Errors like 502 Bad Gateway, Proxy Error, or Error reading from remote server. Invoices stay in “Ready for ERP”.
Solution: Wait for SAP to stabilise. Once SAP is back online, Wello will retry automatically. If the issue continues, ask your SAP admin to confirm the Service Layer is running and not overloaded.
(Ref: What SAP Instability Looks Like in Logs)
What happens in Wello:
Invoices stay in “Ready for ERP”
Business Partners may not sync
Work orders and other records may pause temporarily
2. Wrong or Expired SAP Credentials
Cause: The login details saved in Wello’s connector are outdated or incorrect.
What you’ll see: Connector error messages and no records syncing.
Solution:
Go to Connectors → SAP Business One connector
Re‑enter the SAP username and password
Click Save & Continue
Wello will retry sending the invoices in the background.
3. SAP Server or Network Restrictions
Cause: Firewall limits, network downtime, or routing issues prevent Wello from reaching SAP.
What you’ll see: SAP unreachable or repeated retries without success.
Solution: Ask your SAP admin to check firewall settings, routing, and any recent server changes.
4. Missing Setup Inside SAP
Cause: SAP is missing required data for the invoice, such as Business Partner, Items, Price List, or Tax Code.
What you’ll see: Invoice rejected or stuck in “Ready for ERP”.
Solution: Confirm with your SAP admin that all required data exists and is active. Add missing Business Partners, items, or tax codes in SAP, then retry the sync.
5. Invoices Related to SAP-Originated Work Orders (Advanced Cases)
Some Work Orders in Wello are created from a line on an SAP document. When one of these Work Orders is invoiced, the invoice status depends on the Work Order sync to SAP. It does not depend on the invoice itself.
How the invoice status is updated
When the Work Order is completed, Wello syncs the Work Order back to the SAP document line it was created from. This sync includes the Work Order status and details. Wello then waits for a response from SAP.
When SAP returns a success response, Wello changes the invoice status from “Ready for ERP” to “ERP Imported”.
When SAP returns a failure response, Wello changes the invoice status from “Ready for ERP” to “ERP Error”.
When SAP returns no response, Wello cannot tell whether the update succeeded. The invoice status stays “Ready for ERP”.
Cause: This issue can happen in two situations.
Several Work Orders needed to sync while SAP was temporarily unavailable. The Work Order linked to the invoice was skipped.
The Work Order was synced to SAP, but SAP returned no response.
In both situations, the invoice linked to that Work Order stays in “Ready for ERP” even after SAP is back online.
What you’ll see: The invoice stays in “Ready for ERP”. Other invoices sync successfully.
Solution: Contact Wello Support. Wello Support syncs the Work Order to SAP again. When SAP returns a response, the invoice status is updated.
6. Invoice Reset to “Ready for ERP” Without Updating the Source Work Order
Cause: In some cases: A Work Order is sent to SAP and SAP returns an error. The invoice status is set to “ERP Error”. The issue is fixed, and the invoice status is manually changed back to “Ready for ERP”. However, the Work Order’s modified date is not updated, so Wello does not resend it during the next sync.
Because Wello relies on modified dates to detect changes, the invoice is never retried.
What you’ll see: Invoice stays in “Ready for ERP”, SAP receives no new request
Solution: The source Work Order must be updated so its modified date changes. Once the modified date is updated, the invoice will be retried
7. Stock in Wello Does Not Match Stock in SAP
Where stock is managed in SAP, SAP holds the master figure. Wello receives that figure and then subtracts any articles that have already been recorded in Wello but that SAP does not know about yet. Wello subtracts them straight away, so that the same units are not used twice.
Articles reach an invoice in Wello in two ways, and both reduce the stock figure in the same manner:
A technician records used parts while completing a work order in the Field Service App. Those used parts become lines on the invoice for that work order.
A user creates an invoice directly in the Portal and adds article lines to it. No work order and no technician are involved.
In both cases the articles are deducted in Wello immediately, and they are only deducted in SAP once the invoice has been sent and accepted.
This means Wello is expected to show a lower figure than SAP for a while. The difference is exactly the quantity of articles sitting on invoices that have not yet reached SAP. It is not a synchronisation failure.
A worked example:
SAP holds 6 units of an article at a stock location, and Wello has received that figure.
Two units of that article are recorded on an invoice in Wello. This may be a technician recording them as used parts on a work order, or a user adding two article lines to an invoice in the Portal. The result is the same.
Wello now shows 4. SAP still shows 6, because SAP has not been told yet. Both figures are correct at this moment.
The invoice is sent to SAP.
SAP accepts the invoice, deducts the 2 units, and now holds 4.
That figure of 4 comes back to Wello. Wello has nothing left to subtract, so both systems show 4.
The same sum applies when SAP is already at zero. If SAP holds 0 units and 2 units have been recorded on an invoice that has not reached SAP, Wello shows -2. The negative figure is the same calculation, not a separate problem.
Cause: The difference stops clearing when the invoice carrying those articles cannot be sent to SAP. This is usually one of the reasons already listed above, most often the SAP Service Layer being unavailable at the moment Wello tried to send it. The invoice is left in ERP Error, the articles on it stay deducted in Wello, and SAP never learns about them.
What you will see:
The stock for one article at one stock location is lower in Wello than in SAP, and the gap does not close over time.
The figure in Wello may be a negative number.
The invoice carrying those articles is sitting in ERP Error rather than ERP Imported.
Technicians may not be able to add that article to a work order, because Wello sees no stock available.
Solution: Fix the invoice, not the stock figure. Running a stock synchronisation does not help here, because the figure in Wello is already correct for what Wello knows.
You can do this yourself, without contacting support. Open the invoice that is sitting in ERP Error and set its status back to Ready for ERP. Wello then picks the invoice up again and sends it to SAP. Once SAP accepts it, the invoice moves to ERP Imported, SAP deducts the articles, sends the new figure back, and the two systems agree again.
B. How to Fix Sync Failures
You can try these steps yourself.
Step 1: Check the ERP Connector
Go to Connectors in Wello
Select your SAP Business One connector
(Where to View Connector Setting)
Look at the top for any error message
Step 2: Update the SAP Credentials
Sometimes a simple refresh solves the issue.
Scroll to the bottom of the connector page
(Updating the SAP Credentials in Wello)
Click Save & Continue
Re-enter the SAP username and password
Save
After this, Wello will retry the invoices in the background.
Step 3: Give It a Little Time
Once the connector is refreshed, Wello will automatically try sending the failed invoices again.
If SAP is stable, they will change from “Ready for ERP” to “ERP Imported”.
Step 4: Ask Your SAP Admin to Check the Service Layer
If the issue continues, the SAP admin should confirm:
Service Layer is running
Server is not overloaded
No firewall is blocking Wello
No maintenance or restart was happening at the time
Step 5: Confirm Data Exists in SAP
Check if:
The Business Partner exists
Items exist
Price List and Tax Codes are set up
All required data is active
If anything is missing, SAP will not accept the invoice.
Example Case
A customer reported invoices stuck in “Ready for ERP”. Logs showed repeated 502 Bad Gateway errors, meaning SAP’s Service Layer was unstable. Once SAP returned to normal, all invoices synced successfully without changes in Wello.
Our team can check the logs from that day and could found repeated errors:
502 Bad Gateway
Proxy Error
Error reading from remote server
The remote server returned an error: (502) Bad Gateway
These errors showed that SAP’s Service Layer was unstable for a few hours.
When SAP returned to normal:
The Business Partner synced successfully
All invoices were sent to SAP
Nothing was stuck anymore
The issue resolved without needing any changes in Wello.
C. General Troubleshooting Checklist
Check the connector for error messages
Update SAP credentials
Wait if SAP was unstable (Wello retries automatically)
Ask SAP admin to confirm Service Layer and firewall status
Confirm required data exists in SAP
D. Frequently Asked Questions (FAQ)
Q1. Can I fix sync issues myself?
Yes, you can refresh the connector, update credentials, and check basic settings. If SAP is unstable, waiting usually resolves the issue.
Q2. What should I do if invoices stay in “Ready for ERP” for a long time?
Check connector settings first. If credentials are correct and SAP is stable, confirm required data (Business Partner, items, tax codes) exists in SAP.
Q3. How long should I wait before contacting support?
If the issue continues for more than an hour, or if SAP reports no problems but Wello still cannot sync, contact Wello Support.
Q4. Can missing data in SAP really stop syncing?
Yes. If Business Partners, items, or tax codes are missing, SAP will reject the invoice until those are added.
Q5. What happens if SAP credentials expire?
Syncing will stop completely. Re‑enter the correct username and password in Wello’s connector to resume syncing.
Q6. Why are some invoices stuck in “Ready for ERP” even though SAP is back online?
The invoice may be linked to a Work Order that was created from an SAP document line. For these invoices, Wello updates the invoice status only when SAP responds to the Work Order sync. If the Work Order was skipped during syncing, or SAP returned no response, the invoice does not move out of “Ready for ERP”. Contact Wello Support to sync the Work Order to SAP again.
Q7. I changed the invoice status back to “Ready for ERP”. Why is it not syncing again?
For invoices linked to SAP-originated Work Orders, changing the invoice status alone may not trigger a retry. Wello also relies on the Work Order’s last modified date to detect changes. If that date is not updated, the invoice will not be resent.
Q8. Wello shows less stock than SAP for the same article. Is that wrong?
Not on its own. Wello subtracts articles that have already been recorded on an invoice but that SAP has not been told about yet, so Wello is expected to be lower for a while. The gap should close once that invoice reaches SAP. If the gap does not close, check the status of the invoice and set it back to Ready for ERP if it is sitting in ERP Error.
Q9. The stock for one article is showing a negative number. What does that mean?
It means articles were recorded on an invoice in Wello and deducted while SAP was already at zero for that article and stock location. It is the same calculation as any other difference, just below zero. Find the invoice carrying those articles and check whether it has reached SAP.
Q10. Will running a stock synchronisation fix the difference?
No. The figure Wello holds is correct for the information Wello has. The difference clears when the invoice reaches SAP, not when stock is sent again.
E. Summary
Reason | What You’ll See | What To Do |
SAP unstable | 502, Proxy Error | Wait for SAP to stabilise, retry sync |
Wrong credentials | Connector errors | Re-enter credentials |
Network/firewall issue | SAP unreachable | SAP admin to check network |
Missing data in SAP | Invoice rejected | Add missing BP, item, or tax code |
Work Order skipped, or no response from SAP | Invoice stuck in “Ready for ERP”, other invoices sync | Contact Wello Support |
Invoice reset without WO update | Ready for ERP, no sync | Update WO modified date |
F. When You Should Contact Support
Please reach out to Wello Support if:
The issue continues for more than an hour
Updating credentials did not help
SAP reports no issues but Wello still cannot sync
You see repeated 502 or proxy errors
We can check the logs and guide you further.