My suggestion would be to double check your GMC settings to ensure that you have entered the correct website name. Misspellings could lead to broken landing pages. Also, make sure that your site is not password protected and that you are not directing GMC to a broken subpage on the site.
If you continue to have issues, please share the URL submitted in Google Merchant Center > products > all products > click on the product > scroll to the bottom > final attributes.
However, I’m guessing it’s what @Bluesoft_Design suggested, ie password.