In my case, it was because of the domain/subdomain issue. I had two domains to work with the same credentials and have them both as origins, however my ServerDomain was set to the main domain so that it can work for both.

Later I realized that, in that situation I have to host the assetlinks.json file in the main domain as well.

Example: My server domain: example.com My origins are: subdomain1.example.com, subdomain2.example.com

I was hosting assetlinks.json file for both subdomains like:

subdomain1.example.com/.well-known/assetlinks.json

But it was missing in my main domain, which is still required because it is the main point:

example.com/.well-known/assetlinks.json after hosting it like this, my problem resolved.