The nonce_monitoring parameter of blxr_tx endpoint enables nonce monitoring for transactions.
Tx Nonce monitoring is subject to rate limiting. Tx Nonce monitoring is available only on Cloud-API
Transactions are checked every 5 minutes and are resubmitted if they are no longer presented in the transaction pool
Tx Nonce monitoring is limited to 48 hours and there are a maximum number of 20 attempts to resend a transaction if it disappears from the transaction pool.