Posting key & not defined

What causes this issue?

Service financial accounting: posting keyel "&v1&" was not found in
the posting key table. There are two possible causes for this:
posting key "&v1&" has not been defined in FI customizing
the posting key is supplied incorrectly from the calling application

System Response

System error

How to fix this error?

There are two possible solutions:
define posting keys "&v1&" using the FI customizing functions
system error in the calling application - contact the SAP Hotline
service.

Error message extract from SAP system. Copyright SAP SE.