Before creating your account we run a short automated check that you are a person and not a bot. It usually passes on its own with nothing for you to click.
When it does not, the message is one of two things.
The check has not finished. Reload the page and let it run again before filling the form back in.
The check ran and did not pass. That is nearly always something in the browser blocking it rather than anything you did wrong.
Work through these in order:
Reload the page. The check expires after a few minutes. If the form sat open while you found your referral code, this alone fixes it.
Turn off ad or script blockers for clubaffili.com. uBlock Origin, Ghostery, Privacy Badger and Brave's shields all block the check. Allow the site, then reload.
Turn off your VPN or proxy, just while you sign up. Shared VPN addresses are used by a lot of people at once and get treated as suspicious.
Check your device's date and time. If the clock is wrong by more than a few minutes the check cannot validate. Setting it to update automatically fixes it.
Try a different browser, or a private window with extensions disabled.
Get in touch through How to contact ClubAffili support and say which browser and device you are on, and whether you use a VPN. That is usually enough for us to see what is blocking it.