Once the transaction is confirmed by the user, the transaction information will be relayed to the whole Bitcoin network.
Every 10 minutes, miners compete for the right to validate and process all the pending transactions. If the transaction is valid, it will then be moved to the pool of “Unconfirmed Transactions” for processing. If it fails, this transaction will be marked as “Invalid Transaction” and will not be processed.
After obtaining the right to update the ledger, miners will take around 1000 transactions from the “Unconfirmed Transactions” pool to process. As each block can store only a limited number of transactions, sometimes our transaction may not be processed in time because of an overwhelming number of unconfirmed transactions.