Enter a sender activity type or a group

What causes this issue?

In activity input planning, you can enter either a single sender
activity or a sender activity group. You cannot however enter both
options.

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?

Delete either the single sender activity or the group of sender
activities, or
Enter a value in one of the fields.

Error message extract from SAP system. Copyright SAP SE.