Retry function helps in repeating a function that might not be done due to these reasons:
Mobile battery died
Connection was lost
App was closed in the middle of the transaction
Retrying a function is done by passing the same transactionId of the function executed. Each function has transactionId which is unique, if the same transactionId of a transaction is passed, the transaction will not be created and the receipt will be shown to indicate that the transaction exists. If a new transactionId is sent, a new transaction will be created.
Local Server Concerns
Please note that the checking happens under these conditions:
Checking is happening locally, meaning, if the app is deleted, there's will no be any checking.
Retry should be done within 24 hours of creating a transactions, otherwise, there will be no checking.