When send Bitcoin to the machine do choose Priority Fee from Blockchain wallet.
Normally ATM will dispense cash if you send the right amount of BTC to the machine in a timely manner. (if you adjust the amount or send it late then no cash will dispense). If the machine sense that your transaction might stay ‘Unconfirmed for a long period of time’ then it will ask for your telephone number. After your transaction has 1-2 transactions it will send sms that says ‘Your cash is waiting! Go to the ATM and press Redeem.’ Then you can go to the machine, enter the telephone number and enter the sms then money will dispense. If you don’t redeem within 24hrs then code will expire. Please note to get refund, I need to wait until your transaction has a few confirmations and 24hrs after the code expires.
This normally happens when the mempool is high e.g. above 60,000 unconfirmed transactions. You can check life mempool count from https://blockchain.info/charts/mempool-count
A transaction with low fees can stay unconfirmed up to 80hrs. After that it will either reverse back to the sender or finally made it to the destination. There is nothing one can do to speed it up. Just wait.