How I added Solana Pay USDC to a SaaS app — a real implementation, not a tutorial

Most Solana Pay tutorials are synthetic. Here's the actual code running in production on transpiler.us, a developer tools platform I built solo.
Why Solana Pay instead of Stripe-only
I already had Stripe. But Stripe doesn't work everywhere, and USDC settling instantly with near-zero fees is genuinely better for global users. It wasn't about looking good — it was the right technical choice.
The implementation
The flow: user clicks "Pay with USDC" → backend generates a reference keypair → frontend displays a QR code with the Solana Pay URL → backend polls the RPC endpoint until it sees a confirmed transaction matching the reference → credits are added to the user's account.
No third-party wrapper. I read the Solana Pay spec and built it directly.
[Walk through the key code sections — QR generation, reference keypair, polling loop, transaction verification]
What I'd do differently
Use a dedicated RPC endpoint from day one instead of the public mainnet endpoint. Public RPC rate limits will bite you in production.
The full source is MIT licensed: https://github.com/Jeah84/devtools-platform
Live platform: https://transpiler.us