Records of the payment through official channels, the identity and background documentation submitted, and clear evidence of where the funds came from. Keep them for the same reason any large cross-border transfer is documented: banks, tax authorities and future advisers will all have questions.
Keep the record for the other authorities
Even where a framework does not impose the exhaustive lawful source analysis that the investment programme does, a large transfer to a government generates interest elsewhere. The financial institution moving the money will ask. A Canadian tax adviser will need to know what happened and when, particularly where the funds came from a business the applicant still holds.
A future adviser looking at the family's overall position will want the chronology. So keep the sale or distribution records, the account statements showing the transfer, the receipts issued through the official channel, and the correspondence. Store them with the immigration documents rather than separately.
On mechanics, be deliberate: use only the payment routes the programme identifies, and treat any intermediary offering to handle the payment, accelerate the process or guarantee an outcome as a reason to stop. No third party can guarantee a United States immigration result. Hypothetical example: an independent documentary producer wants to rely on professional achievements for an underlying immigrant classification.
The first review produces a document index connecting each claimed criterion to a primary record: awards, contracts, press coverage, credentials, and identity documents. Original or certified records settle the achievement; a payment receipt alone settles only that money moved. The applicant should collect records while organisations can still verify them and retain translations where needed.
A disorganised file often fails because it asks an officer to infer the category from a résumé rather than presenting evidence mapped to the applicable standard.