A first review needs a chronological record. Useful documents include player contracts and amendments, registration data, club notices, training and match records, transfer or loan agreements, association correspondence and payment demands. For minors, the communication with parents or legal representatives and the documents used at the time should also be preserved.
Training clubs should keep records that allow an independent reviewer to follow the club history. Receiving clubs should examine a demand not only by its stated amount but also by its legal basis and calculation. Players and families should keep letters with response requests in an organised file rather than forwarding isolated messages.
A short timeline is helpful: which club was involved and when, when was the player registered, which transfer is now at issue, is there a later international transfer and which authority requested which information? These questions often separate the two mechanisms at the first stage.