Solution : https://service.sap.com/sap/support/notes/431181 (SAP Service marketplace login required)
Key words : 
additional key words abp, budget billing amount items, budget billing amounts, budget billing plan, function group ea61, field rea61-mahnv, modification group gruppe2, prerequisites note 430283 solution, dunning procedure field, dunning procedure entered
Related Notes : 
       
| 454714 | BBP: Changing budget billing plan item after dunning notice | 
| 435980 | Budget billing plan: Set dunning procedures |