It sounds likely that you have made a disbursement payment (DPU) instead of picking up and paying your Billed Anticipated Disbursement (DUB). This is easy to resolve, by following the steps below:
Pick up and pay the DUB, either from Client Postings, Pay Unpaid Disbursements, or from Purchase Ledger, Pay Supplier.
Go to Client Postings, General Postings and post a negative DPU (when entering a value in the Net box precede the value with a -).
Go to Client Postings, Bills and pick up the DPU from the Add Disb button and Post the bill.
Go to Client Postings, Allocations and tick off the negative and posting bills, then click Allocate.