Your withdrawal address gets locked for 24h after you first use it, this security feature was implemented so in case somebody got access to your account they couldn't withdraw your coins right away if you didn't whitelist your withdrawal address(es).
If you have 2FA activated on your account, your withdrawal address will not get locked after the first use. However, if you initiate a withdrawal address change it will get locked for 24h once you confirm the change via email.
In order to change the withdraw address please follow these steps:
2. Tap on your picture in the top right corner of the screen.
3. Tap on "Wallet"
4. Tap on "Withdrawal addresses"
5. Here you can change your withdraw address for each coin, please note that once you change it the address will be locked for 24h, after which you can withdraw your coins to it.
6. Select the address that you wish to change and input the new address that you wish to use. Click on the "Confirm" button.
7. An email will be sent to the email address under which your account is registered where you will be able to confirm or deny the address change. If you did not request the change, you're also able to freeze your account with a button in this email.