Screen by screen
What the user experiences: they confirm a quote, send one ordinary transfer from their own wallet (yours can prefill it), and watch the order move through a few states until the settle token arrives at their address, with no approvals, no signup, and nothing unusual to sign.
The deposit screen is where your design effort goes. Make the exact amount, the address, and the countdown impossible to misread, because funding the order is the one step only your user can perform.

