Opinion: I suspect it is not a problem because the transaction only occurs when you make payment.
On a related note, where can I find a copy of a shtar mechira for a web-based business (where certain transactions for e-products may occur on shabbos)?
I understand the use of a shtar mechira is discouraged (at least in the case of a real business where melocho is being done by worker) but are the other better solutions?