Why was my email address rejected when claiming a page?

The claim flow only accepts an email on the same domain as the tool's own website, because that is what proves you represent the vendor.

Two cases get turned away. Free consumer addresses like Gmail, Outlook, Yahoo and similar are rejected outright, since anyone can create one. And an address on a domain that does not match the tool's website is rejected even if it is a company address, because it does not prove anything about this product.

There are legitimate edge cases. Some companies run their product on one domain and their email on another, and some smaller teams do not have company email at all. If that is you, email hello@topalternatives.to from whatever address you do have and explain the situation. A person will look at it.