Cannot upgrade to paid subscription

I'm trying to upgrade Projects to a paid subscription so that I can add it to other apps already in my account (earlier today I successfully upgraded CRM to a paid plan in this account).

In Projects there's a link "You have reached the maximum limit. Upgrade to do more." but when I click it, it says "Contact your project administrator to upgrade!".

Well, I'm the project administrator. Earlier today I deleted another Zoho unused account from my company, would that be the reason why this happens?

How can I fix this? Thanks.