Before. The investment must already be committed when the application is judged, so the agreement should be signed and funds paid or placed in escrow that is conditional on visa issuance. Signing after the interview leaves nothing to assess.
Commit first, but commit in a way that can be unwound on refusal
Hypothetical example: a Mission contractor wants to keep his options open by attending the consular interview before signing anything, then closing if the visa is granted. That order fails, because a treaty-investor application is judged on capital already at risk, and an unsigned deal is a plan rather than an investment. The recognized way to protect himself is to sign, pay what must be paid, and place the balance in an escrow that releases to the franchisor on visa issuance and returns to him on refusal.
He should negotiate that structure with the franchisor early, since not every franchise system offers it, and align the lease and vehicle purchases with the same contingency where possible. Applications proceed at the consulate's scheduling pace, so the timetable should assume months, not weeks, between signing and starting work. Hypothetical example: A Canadian artisan-chocolate producer wants to announce a U.S.
storefront opening before its lease, equipment order and escrow instructions are complete. The first review should order the steps: form the entity, sign the transaction documents, commit qualifying funds under terms that expose them to loss, then present a coherent application. The lease, invoices and escrow agreement settle whether the capital is truly committed.
Waiting until after visa issuance to make the essential purchase leaves a plan, not an investment. Build time for consular processing and avoid making business promises that depend on an approval date the investor cannot control.