In short, there are 2 ways to sell. Option 1 is you visit this site and send your crypto on the website. Then you will receive an SMS saying that the cash is ready for collection, you come to the BTM, you enter your phone number and receive the cash. This option is quicker because you pre-sell the crypto.
Option 2 is you come to the BTM, enter your phone number, send crypto to the QR code shown on the screen, wait for 2 confirmations on the blockchain, receive an SMS saying that the cash is ready for collection, you enter your phone number on the BTM and receive the cash. This option is slower and may require you to wait 10-30 minutes for confirmations.