Hi,
As of my knowledge, there is no option in standard if you want to trigger the message automatically only for subsequent debit. I think a custom routine will be the solution in this case. Please check the documentation for the routine 181 and create a custom routine to check the transaction type. Assign the same against the condition type in the message schema.
Assign the access sequence for the condition type and create condition record in MRM1 transaction.
If you need the REKL output to be triggered automatically irrespective of the transaction type, remove the routine (181) assigned to the REKL output type in the message schema in the path: OLMR - Message Determination - Maintain Message Schemas, for the schema MR0002. You may cross check the settings with note: 129643 - Invoice verification: Creating message records
Regards,
AKPT