Duplicate without user-selected canonical

Hi All. Looking for some advice.

Every site I have launched to-date has been with a www. prefix. When setting up custom domain, followed VZY instructions, i.e. A records for both www. and @ to point to 37.16.10.106 BUT when Google Console indexed the site(s), the following error comes up:

New reason preventing your pages from being indexed. Search Console has identified that some pages on your site are not being indexed due to the following new reason: Duplicate without user-selected canonical. If this reason is not intentional, we recommend that you fix it in order to get affected pages indexed and appearing on Google.

Any ideas as I assume I am doing something wrong?..

Best
Steve

Anyone got any ideas please as this is impacting several client websites now…