Duplicate canonical tag issue

[MudassirSultn]

i have this site https://www.dealsmango.com/ which i have selected for canonical , but google is still selecting  my old website https://www.selldealsmango.com/ , i have removed everything from old site only one page with new site link, and also put 301 redirect , but still when i click on request for indexing on google search console same error appears regarding duplicate canonical tag .

what should i do?

remove the canonical tag from old site which i don't want google to index, or what will be the best possible solution.

[MudassirSultn]

Sir ,

Thank you for replying, i will explain step by step what i have done;

Old site: https://www.selldealsmango.com/

New site: https://www.dealsmango.com/

first i have remove all pages from my old site, than only home page left, i then remove all the data from home and on that blank page i posted the new site URL. by clicking on that old site URL you will know what i am trying to explain. but i am using canonical tag  for old site also.

than i have generated XML site maps of both sites and uploaded on google search console. after that i request for indexing and duplicate canonical error occurs.

in 2nd step i have put 301 redirect from old site to new site and than again i have request for indexing but error remain the same.

[effectdigital]

Oh dear this has gotten into a bit of a mess!

For a start, there's an error in your question which may be causing your to get fewer than average responses. You have embedded two links which look like they point to different pages, but you have encoded both the links in your question to point to exactly the same site (even though the text says they should be going to different URLs). This may be confusing people whom are seeking to answer your question

These are the real links for anyone who runs into this:

Old site: https://www.selldealsmango.com/

New site: https://www.dealsmango.com/

Where you say: "I have this site https://www.dealsmango.com/ which i have selected for canonical , but google is still selecting  my old website" - no, you have not fully selected the new site as canonical, as the old site (here) does NOT canonical to your new site, instead the old site still canonicals to itself. The new site canonicals to itself to, but the old site does NOT canonical to the new site

https://d.pr/i/P70o8N.png (screenshot)

Where you write: "only one page with new site link, and also put 301 redirect" - you have contradicted yourself. You say there is a 301 redirect, but also say the page is still up with a link on it. If there were a 301 redirect, all users and bots would get redirected before the page loaded and you would never see the link (at all) as pages which redirect cannot support any source code

The fact that the page is still live with a link on it, means that there is NO 301 redirect. Maybe you have redirected some sub-pages, I don't know. But your homepage is your post important page, so failing to 301 redirect that (which you have not done) is a big error. Fix that ASAP if you do nothing else

Also make sure you use Google's change of address tool from within the old property's Google Search Console dashboard:

https://support.google.com/webmasters/answer/83106?hl=en

Even if you follow all of these steps, it may take a long time for performance to return now. That's because this migration was handled in a very strange way, what's done is done

Fix what you have implemented with a proper 301 redirect migration project down to the granular (A-to-B) URL level including historic URLs which you can pull from backlink destination data, as well as from Search Console (or analytics by blending the hostname and landing page dimensions)

You'll have to just hope for the best!