CBP seized cash at airport (CAFRA) — asked for more proof of source/intended use. What’s reasonable to submit?

Hi all, looking for general guidance (I have a lawyer). CBP seized ~$20,000 at Philadelphia airport for an alleged currency reporting violation (FinCEN Form 105 issue). I filed a petition for remission/mitigation under CAFRA. CBP reviewed it and sent a letter asking for additional documentation showing: legal source of the funds, and legal intended use. The money was a mix of family funds and gifts (including from my Uncle) and was intended for living expenses and home repairs overseas. Most of it was saved in cash over time. No criminal history.

My question: In CAFRA cases like this, what types of documents are typically persuasive to CBP when there isn’t a perfect bank trail? Are affidavits + property/repair documents generally sufficient, or is something else usually expected?

Not asking for legal advice specific to my case—just trying to understand what’s considered reasonable/standard. Thanks.