Stripe & UPS Integration Fix

My Base44-powered marketplace is live but payments and shipping still need real-world functionality.

Stripe
• Every new user must save a credit card during sign-up and pass Stripe-based identity verification.
• When someone wins an auction the card on file is charged automatically; no manual checkout should be required.
• “Buy It Now” has to run through the same flow for an instant charge.
• Users must be able to swap a card at any time, with the new one verified before it becomes active.

Shipping (UPS API)
Sellers will enter weight and dimensions for each active listing from their dashboard. When a buyer types a ZIP code on the listing page, the site should call the UPS API, calculate the quote from the seller’s stored ZIP to the buyer’s, add a 25 % markup, and display that estimate. At checkout the system should re-confirm the rate and apply the actual charge.

Tech notes
• Codebase: Base44 site (built on standard HTML/CSS/JS with a Node back end).
• Clean, well-commented code that I can maintain later is important.
• Security and PCI compliance are non-negotiable; please lean on Stripe’s built-in tools wherever possible.

To be considered, send a concise proposal that shows how you will hit the three key Stripe features—identity verification, auto-charge on win, and card replacement—plus the UPS rate calculation with the 25 % uplift. Links to comparable projects or short code samples are welcome.