Submit the application and nonrefundable processing fee, then follow the USCIS email instructions for Form I-140G and any supporting documents. Keep identity and family information and a dated copy of the official terms ready, but do not describe an EB-5-style lawful-source file as a published Gold Card requirement.
Prepare it like an immigrant case, because it becomes one
The official FAQ says that after the initial application and processing fee, USCIS emails instructions to complete Form I-140G with supporting documents; USCIS and the Department of State may request additional information. It does not publish a universal list of civil, police or lawful-source documents, so an EB-5 source-of-funds file should not be presented as a stated Gold Card requirement.
Hypothetical example: a Lac-Beauport applicant funding the gift from a professional-practice sale should follow the official requests and retain transaction and payment records without assuming that EB-5 evidentiary rules automatically apply. Save a dated copy of the official page and FAQ as they read on the day of submission so the terms relied on can be identified if they later change.