although i have never worked on payment systems directly but based on my limited exposure and knowledge, i will try to explain how the payment system works.
Broadly, there are 3 parties involved here, remitter bank, National Payments Corporation of India and Beneficiary Bank.
You were doing a transaction from Remitter Bank Account (your account integrated with PhonePe app) to Beneficiary Bank Account (which is the Niyo IDFC account). Technically speaking at a very high level, you give the command to remitter bank through PhonePe app to transfer funds to Beneficiary bank. There could be some other parties involved as PhonePe is not itself a bank and leverages Yes bank’s and ICICI bank’s infrastructure in transactions but we can refer to them as PhonePe’s system for simplicity. On your request, PhonePe debits the amount first and forwards this request to NPCI and NPCI issues a RRN Number (unique identifier of the transaction) and forwards this request to Beneficiary bank to make credit in the account.
PhonePe is supposed to issue you RRN number received from NPCI for every such transaction. If PhonePe did not issue any RRN number to you, it is very likely that transaction did not reach to NPCI systems. You need to check with PhonePe if you don’t have any RRN number. If RRN number was generated, that means the transaction was initiated by PhonePe and it reached NPCI as well but still the status of the transaction could not be known. PhonePe will have access to the systems which can tell the status of any transaction by searching using RRN number. If they find it a failure, they have to return it to you. If they say, it’s a success, then you need to check with beneficiary Bank along with the transaction details, which is us.