I’m building a small stand-alone module around an ESP32 and need it to do one thing flawlessly: verify UPI payments made through PhonePe, google pay, bharat pay etc. The flow I have in mind is straightforward—customers scan a QR code, complete the transfer in their PhonePe app, and the ESP32 instantly confirms that the payment succeeded before triggering the rest of my system. What matters most is rock-solid transaction verification. The device must generate or display a QR code, listen for the incoming callback from PhonePe (or poll, if that is the only option PhonePe’s API allows), parse the response, and expose the result locally (GPIO change, serial print, or MQTT publish—I’m flexible on that detail as long as it is reliable). No receipt printing or push notifications are required; I only need a clear success/failure confirmation along with the amount and transaction ID. I already have the hardware (ESP32-WROOM, 2.4-inch TFT, and internet connectivity via Wi-Fi). What I’m missing is the firmware plus the exact API integration steps, including any necessary checksum or signature verification PhonePe might demand. If you prefer working in the Arduino framework, that’s perfect, but ESP-IDF is fine too. Deliverables: • Fully commented ESP32 source code that performs QR-based PhonePe UPI verification and returns a boolean success status, amount, and transaction reference ID. • Setup guide covering PhonePe merchant account registration, API credentials, and webhook configuration so I can reproduce the process on additional devices. • Short demonstration video or log captures showing a live payment being detected and confirmed. Acceptance criteria: the device must detect a successful PhonePe payment within five seconds of completion and have a false-positive rate of zero in my test environment. If you have already handled UPI or PhonePe integrations on embedded hardware, that experience will be invaluable.