How does NPCI manage the UPI Payments ecosystem?

From my understanding NPCI is the developer and manager for UPI. The NPCI-UPI site mentions that there are the following stakeholders in the UPI ecosystem. How exactly do they interact during a transaction and settlement flow?

  • Payer PSP (My understanding - Payment service provider like GPay, PhonePe used by Payer)
  • Payee PSP (My understanding - Payment service provider like GPay, PhonePe used by Payee)
  • Remitter Bank (My understanding - Bank of Payer, from which amount is deducted)
  • Beneficiary Bank (My understanding - Bank of Payee, to which amount is deposited)
  • NPCI (Developer of UPI and manager of new entities that interact with UPI apps like PSPs, BOUs, COUs etc.)
  • Bank Account holders - who are these account holders, if not the payer’s/payee’s/merchant’s?
  • Merchants (My understanding - Business that uses UPI links to collect money from customers)

So then, once the above definitions are clear, I have the following questions:

  • How do PSPs get authorisation to integrate with UPI network?
  • How does NPCI get banks to be onboarded and integrate with the uniform specs it has provided? Are there UPI apps for all banks?
  • How do Merchants get added onto UPI?