It is valid long-term.
Static QR Code Design: Your default Receiving QR Code is permanent and fixed. It will not expire when you close the app or over time.
Supports Repeated Use:
You can safely save it to your phone's photo album and send it to different friends multiple times.
Business/Offline Scenarios: You can even print the QR code and display it in offline stores or at checkout counters for long-term "Scan & Pay" convenience (provided the payer is also an MPChat user). There is no need to generate a new code for every transaction.
Note: Even if you have set a "Specific Amount" for a QR code, the generated image remains reusable for as long as you need it.