No IDoc selection possible (too many IDoc types); enter IDoc directly

What causes this issue?

More than 15 IDoc types are assigned to the selected message type &v1&.
For technical reasons, IDoc selection is no longer supported.

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?

Please select an IDoc type directly.

Error message extract from SAP system. Copyright SAP SE.