When you deposit, the bookmaker's payment processor sends an authorisation request through Visa or Mastercard to your bank. Betting transactions carry a specific merchant category code (7995), which lets banks recognise and block them. If your bank approves, the funds are credited instantly.
Withdrawals depend on the processor supporting original credit transactions (Visa Direct or Mastercard Send). Where that is not available, the bookmaker may refund only your deposited amount to the card and ask you to take winnings by bank transfer, e-wallet or crypto.
Debit versus credit
Debit cards spend your own money. Credit cards may treat a gambling deposit as a cash advance, charging a fee and interest from day one.