Settlement canceled, as & sender has messages > spool list

What causes this issue?

Messages have occurred for &V1& senders. The system has terminated
processing.

How to fix this error?

Look at the spool log for the job to see which messages have occurred.
Correct the circumstances which caused the message or narrow the sender
selection.
If you cannot clear the causes of the messages or cannot use selection
to filter out the defective senders, the only remaining option is to
reduced the number of senders selected by background job, so that a
maximum of 998 senders per background job have messages.
Example:
In internal order settlement, the message "Maintain the sender
settlement rule" appears repeatedly.
If you use a status selection profile in the selection variant when
selecting orders, you can stipulate there that only orders with
settlement rules (system status SFMT or SETC active) can be selected.

Error message extract from SAP system. Copyright SAP SE.