Miners typically pick the transactions that pay the most fees and include these in their blocks first. Posted by, i've just opened my first wallet, and chose to open it with blockchain. When I tried to purchase some bitcoin, I got the following message after I input my payment details: Transaction Rejected, your purchase was rejected after being flagged by an automatic risk evaluation. Unfortunately, the reason cannot be disclosed due to security regulations. (In fact, transactions with lower fees or even no fee at all were often included as well.). Promotions in weekly thread only, help keep our sub clean! 18 comments 100 Upvoted, this thread is archived. For less urgent payments, you can include a lower fee; it will just take a bit longer to confirm. The Transaction ID can be copied from the error reporting URL: It may take longer than usual for low priority transactions to get confirmed (expect hours to days depending on the amount of unconfirmed transactions). And as not all transactions can be included in the blockchain straight away, backlogs form in miners mempools (a sort of transaction queue.).