I'm trying to sync a supplier to our ERP (Enterprise Resource Planning), but due to an error in the bank information saying that information is missing in the ERP side, I can't complete the sync.

First of all, you have to identify what is/are the missing question(s). To do so, do as follows:

1. Export all documents in your supplier registration template where you have bank information.
   1. Remember to do so for all versions of the registration template which have been applied to the affected suppliers through template upgrades.
2. Open them in a spreadsheet editor, such as Microsoft Excel, and look for the bank info questions.
3. Compare all bank info questions between versions, and look for anything missing in a subsequent version, which was present in the previous one.

After this is done, there are 2 options:

1. Add questions with the missing field mappings as needed back in your registration template and run a template upgrade so the change is applied to the affected supplier.
2. Check in your ERP if the validation for this bank info can be made not required, and then make it so.

The likely cause of this is that between versions of your registration template used in the affected supplier (from where the bank information is coming), a question with a bank field mapping has been removed.
After a template upgrade is done, if a question has been removed in the applied version, it'll get removed from the affected suppliers and this can create sync problems.

In case you want to know more about integration between SLP and ERPs, please refer to the Supplier management setup and administration guide, under section Topics about managing supplier data integrations with SAP ERP systems.

SAP Integration Suite Managed Gateway > Managed Gateway for Sourcing Integration > Managed Gateway for Sourcing Supplier Mgmt