Arrangements can only be created in the 'Change' mode for the promotion

What causes this issue?

You are currently in the "Create promotion" mode. However, creation of
promotion arrangements is not permitted in this mode, as a promotion
number has not yet been assigned, or the promotion number you entered
has not yet been saved.

System Response

Creation of promotion arrangements is blocked.

How to fix this error?

First save the newly created promotion and then maintain the promotion
in "Change" mode.

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.