When your customer pays a bill, the transaction request is received at Paytm's server and there are multiple validations carried out such as: valid source of request, structure of request, uniqueness of request, etc. Once these validations are passed, a transaction is created.
Customer fills basic payment details to authorize the payment. Once the authorization is successful, money is debited from a customer’s account. This transaction is a successful transaction.
If the customer drops out from the payment process or in the event of payment authorization failure, money is not deducted from a customer’s account. This is marked as a failed transaction.
Sometimes Paytm doesn't receive real-time transaction status from the bank. This can be due to many reasons such as network issues, technical errors at customer's/bank's end etc. This is marked as pending transaction. Refer this for detailed handling of pending transaction.
Payments received against successful transactions are credited into your bank account on T+1, where T is the date the transaction successfully completes. Once the payment is credited, corresponding transaction is marked as Settled.