Check that your email app hasn’t changed or cut off part of the verification URL. itch.io will reject the URL if it’s been modified. Try copying the complete, original URL from the email and pasting it directly into your browser’s address bar.
Verification links also expire, so request a new verification email and use the link soon after it arrives.
If a fresh, unchanged link still says it’s invalid, let us know which email app and browser you’re using and the exact error text. Please don’t post the verification link or token.