Partner &1 account &2 is locked for posting, locking reason '&3'

What causes this issue?

For business partner &V1&, a <LS>posting lock</> type of business
partner lock has been entered. This lock makes postings impossible for
all business partner contract accounts (and thereby also for contract
account &V2&).

System Response

Error message. The wanted document cannot be posted.

How to fix this error?

If you do not wish to retain the posting lock, reverse the lock. Reverse
the business partner lock under: <LS>Master Data -> Business Partners ->
Process Business Partner Locks</>.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.