Try path from SPRO-IMG-Financial Accounting (New)-Accounts Receivable and Accounts Payable-Business Transactions-Outgoing Payments-Outgoing Payments Global Settings-Payment Block Reasons-Define Payment Block Reasons.
Additionally there are many img paths to maintain the payment block reason, check my blog post Find IMG path from F1 help for a field
You can use the field MIRO-Payment tab-Pmnt Block-F1
***Edited by: Dibyendu Patra