Assign at least one document from an SAP TM

What causes this issue?

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

System Response

You want to post directly to a general ledger (G/L) account.

How to fix this error?

Choose a reference document from SAP Transportation Management (SAP TM)
so that the system can determine the creditor. To do this, choose the
<LS>TM</> tab page and enter the document number. At least one TM
document item must be selected for settlement before you can post to G/L
accounts.
Choose the <ZK>G/L Account</> tab page and enter the required data.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.