Keep the signed engagement letter, the invoice, proof of payment, and the account statement showing where the money came from. Add correspondence describing what the broker will deliver. These records support later questions about the path of funds and about how much preparatory spending relates to the eventual enterprise. Decide who holds the master copy of the funds file, and keep one. Where two spouses pay from different accounts, or a company account is used for a personal commitment, the trail forks and someone has to be able to explain each branch. Name that person now.
Build the funds trail before it is needed
A statement showing a balance does not explain how the money was earned or how it reached the payment account. Collect the underlying evidence while it is easy to obtain: employment or business income records, sale proceeds, gift documentation, or loan agreements identifying collateral. Gaps found later can often be filled with additional evidence, though older transfers are harder to reconstruct.
Ask which items your reviewer considers weakest right now. One record settles a question no bank statement can: the instrument that gave the investor the money in the first place. A sale agreement, a dividend resolution, a deed of gift or a loan agreement naming its security each explains an origin.
Collect the instrument alongside the transfer confirmation, because a pair of documents agreeing on amount and date is worth more than either alone.