A dated copy of the official program page and its questions and answers, read personally rather than relayed. Alongside it, the evidence supporting the underlying EB-1 or EB-2 classification, because that is where an application succeeds or fails once the payments have been made.
Keep the page you relied on, with the date you read it
Hypothetical example: Bastien has been shown the framework's figures secondhand and wants a record of the terms he actually relied on. Two files are worth building. The first is a verification file: printed or saved copies of the official page and its answers, each stamped with the date of retrieval, plus written confirmation from an attorney of the amounts and process current on that date.
This is unglamorous and it is the file that protects Bastien if terms change between his decision and his payment, or if somebody later tells him something different. The second is the substantive file for the underlying classification, and it looks like any employment-based immigrant file: evidence of his role and its scope, the company's records, qualifications, and whatever the specific classification requires. Two documents are worth refusing rather than collecting.
Payment instructions delivered by message or attachment should never be acted on without independent verification through the official channel. And any written guarantee of an outcome is a reason to stop, because nobody can give one.