Fix Broken PayPal Integration for User Upgrades (PHP Website

Job Description: I need an experienced PHP developer to fix a website’s PayPal payment system that handles user upgrades (subscriptions or one-time upgrades to premium accounts). The PayPal upgrade/payment flow previously worked but has stopped functioning. Users can no longer complete upgrades successfully.What I need:Diagnose why the PayPal upgrade process is broken Fix the integration so users can successfully upgrade again Test the full flow (payment → confirmation → account upgrade) Ensure the solution is secure and follows current PayPal best practices Provide a brief explanation of what was wrong and what you fixed Tech stack & access:PHP (custom or framework-based site) PayPal integration (could be older IPN, NVP/SOAP, or REST API) I will provide full access to the code, server, database, and PayPal account after hiring Timeline: Prefer someone who can start within 24–48 hours and finish in 1–3 days.Please include in your proposal:Relevant experience with PayPal + PHP integration's (especially subscriptions or account upgrades) Examples of similar payment fixes you’ve done Your estimated timeline Whether you prefer fixed-price or hourly Required skills:Strong PHP experience PayPal API / payment gateway integration Debugging payment flows Experience with user account / membership systems is a plus Looking for someone reliable who can communicate clearly and deliver a working solution quickly. Prefer the most reliable minimal fix first (full rewrite only if truly needed).