Stripe subscription renewal not resetting quota - Next.js + Supabase

Hello! I run a small astrology app - people ask it questions and get answers drawn from their actual birth chart, with a Python service doing the astronomy behind the scenes. It's live, it has paying members, and it's very much a one-person business with developers helping me out along the way. I've got two things that need fixing. I should also say I'm hoping to find someone I click with, because small jobs like this come up every couple of months and I'd rather build a relationship with someone than start from scratch each time. The first one is costing me money and goodwill. Paid members are meant to get 500 "asks" a month, resetting each time their subscription renews. New signups work fine, but on renewal Stripe charges the card and the balance never tops back up - so people are paying and getting nothing, which I'm not comfortable with. My hunch is the webhook handles new signups but not invoice.payment_succeeded for renewals, though I'd rather hear your read on it. The affected accounts need correcting too. The second is a model that's been quietly failing since June. Something in the codebase still calls claude-sonnet-4-20250514, which Anthropic retired on 15 June 2026. I don't yet know which feature it powers, so part of the job is finding out, then migrating it to claude-sonnet-5. It's not a one-line swap - temperature, top_p, top_k and assistant prefilling all return 400 errors now and need removing or replacing. Anthropic's migration guide covers it. The stack is Next.js / React, Supabase (auth and Postgres), Stripe for billing, deployed on Vercel, using both OpenAI and Anthropic. One request - rather than a CV or a portfolio, I'd love to hear what you reckon is causing the first problem and how you'd confirm it. That tells me far more than a list of credentials, and it's genuinely how I'll be choosing. Looking forward to hearing from you!