Google:
Transactions happen this way.
Transaction request.
POS - acquiring bank - Visa/MasterCard/Rupay - issuer bank
Transaction response takes the reverse way from issuer to POS
In this journey if transaction request go successfully to issuer then issuer will send a confirmation message on registered mobile number but while the response coming back to POS for any reason if the connection fails then POS response will be unsuccessful. Hence you see a failure message on POS.
Anyways this kind of transactions are again credited back to customer by issuer bank this is called reversal.