Full Stack Developer To Help With Some Changes On My Websites Accounting

We asked our current developer agency to connect us to a clients api it was suppose to be done by 11th February it’s still on going right now they have completed everything bar leaving our accounting system a mess they have canceled orders moving to invoices which is not legal in the uk they won’t fix it unless we pay we found the below work around to save time and they won’t pay it so I offered to pay it and then they upped the price again so getting fed up now I would like a quote to have my accounting correctly done where cancled orders do not go to invoices also quote for the below thanks Retain Invoice Values: Canceled invoices must show their original positive transaction values in the invoice area; they must not be set to £0.00. One Reversal Per Order: Exactly one matching refund row is to be generated per canceled invoice. There must never be multiple refund rows for a single failed order / cancelled invoice. The "R-" Prefix Matching: The generated refund row must explicitly use the exact same invoice number but with an "R-" prefix (e.g., Invoice 2489 must generate a corresponding refund row numbered R-2489). Data Proximity (Nesting): The original canceled invoice row and its corresponding R- refund row must display and export directly next to each other (one immediately after the other) with no gaps or unrelated data between them. Timestamp Mirroring: The R- refund row must inherit the exact same Date and Time as the original canceled invoice to ensure they stay grouped together when sorted chronologically. Negative Balancing (Amount & Profit): When exported, the canceled invoice row must show its positive value, and the matching R- refund row must show its corresponding negative values for both the Amount and Profit columns (e.g., $4.20 and -$4.20). This ensures they perfectly net to £0/0 when exported like wise for profit which I believe will be set to 0 so should be ok. Visual Indicators (Red Text): On the export files, the entire text row for both the Canceled invoice and the R- Refund row must be highlighted in red for clear operational visibility.