Your reward is withdrawable as soon as it is in your Host wallet (normally about 3 days after your referee's listing is published) - you just need to set up your Stashbee wallet, if you haven't already, and you will be able to withdraw. You can do this here.
When doing this, you may be asked to verify your bank account. This is an additional verification step, which ensures our payment provider, Stripe, is compliant with Know Your Customer (KYC) or Anti-Money Laundering (AML) obligations. Not fun, we know, but it helps to improve security and prevent fraud.