Check that the form sharing settings are set properly. Only people with the link that you provide should be allowed to access the page.

Edit the title of the page with a unique title, as the system automatically discards a page with a title that is duplicated.

Often times, the swap limit given to the user has been reached. Try deleting other pages within the form to free up a space for a new page.

If none of the above apply, check if the advanced settings on the form are set to enable the page.