Transactions cannot be stacked (or ‘nested’), so you cannot start a new transaction within one that has not been validated or canceled.

Sets and record numbers have no usefulness within transactions with respect to records added or deleted within the transaction.

Do not start a transaction in the After phase (On unload form event) of a record.

Do not forget to end your transaction with a VALIDATE TRANSACTION, as everything you have done within it in a process will be lost when the process ends.