Are you 18 years old or older?
You must be 18 years or older to submit content to Adobe Stock account.
That's just the thing. I am over 18, my account says I'm over 18, bit it won't let me through.
Contact support (footer of the web-page) ! Account issues can't be solved here.
Check your Adobe ID. If you indicated you are under 18 when setting up your Adobe ID (different from your contributor account) the system won't allow you to create a contributor account.