Field help (DUDUMRNUM) 

The "Mandate reference" field is used to initialize or select the mandate reference, which is the unique mandate identifier. This field is initialized with the validated main mandate of the company/pay-by BP combination. If there is no validated main mandate, the field is empty but another validated mandate of the combination can be selected.

The user can modify the payment method. If the chosen payment method is SDD, the mandate reference can be accessed and the user can select the reference desired. If the chosen payment method is other than SDD, the mandate reference is not displayed and the field can not be accessed.

SEEINFO  

This field can be accessed for the current company only if activity codeSDD - SDD managementis activated and parameterSDDMGT - SDD management (chapter TC, group SDD) is set to "Yes". Moreover, the payment method selected must be SDD.