Posting not possible in current document with this trans.type

What causes this issue?

This transaction type manages proportional values, in contrast to the
transaction types with which postings have been performed in the
current document.

System Response

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

How to fix this error?

Close the document. Post the transaction using another transaction
type.

Error message extract from SAP system. Copyright SAP SE.