1. The Unified Payments Interface URI Format
The National Payments Corporation of India (NPCI) standardizes UPI payment QR codes using the `upi://pay` custom URL scheme:
upi://pay?pa=merchant@upi&pn=Store%20Name&mc=5411&tid=TX123456&tr=INV001&tn=Payment&am=150.00&cu=INR
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Key URI Query Parameters:
*
`pa` (Payee Address): The verified Virtual Payment Address (VPA) / UPI ID (e.g., `name@okaxis`, `store@icici`).
*
`pn` (Payee Name): The legal or trade name of the recipient (URL encoded).
*
`mc` (Merchant Category Code): Optional 4-digit code identifying business type.
*
`am` (Transaction Amount): Fixed payment amount (e.g., `150.00`). If omitted, the payer enters the amount manually.
*
`cu` (Currency Code): Strictly `INR` (Indian Rupee).
*
`tn` (Transaction Note): Memo or invoice note visible to both parties.
