AMP Page URL is missing a canonical tag
This means that the URL in question is an AMP Page URL, which does not contain a canonical tag.
Why is this important?
The canonical tag is a mandatory element for AMP pages to be considered valid, and the canonical tag is supposed to point back at the original 'non-AMP' version of the page. If the page is standalone AMP, then the canonical should be self-referential.
If no canonical exists, search engines may not consider the HTML valid and may not index the page properly or include it in search results.
What does the Hint check?
This Hint will trigger for any AMP Page URL that does not contain a canonical link element in the HTML or the HTTP header.
How do you resolve this issue?
Add a canonical on the AMP page so that it points back to the non-AMP version of the page, and ensure that the non-AMP version of the page has a self-referencing canonical. It should look like this:
For the URL: https://example.com/page-a/
This page defines a self-reference canonical and an AMP page:
Then the AMP page has a canonical pointing back at the non-AMP page:
If we have a standalone AMP page, say https://example.com/page-b/amp/, in this case the canonical should be self-referential.