Automatically create <branch>.mydomain.com subdomain?

I have my domain managed with with Netlify DNS and I have configured the builds so every new branch gets automatically deployed. But I need to manually go to Domain management > Branch subdomains to manually create the domain, is there a way to configure it to be created automatically or an API that I can call to set it up?
Thanks

Can you share the domain you are seeing this issue on? It might be that you have not changed the name servers for your domain. If you happen to be using Route53, you can follow this post: [Common Issue] I changed my name servers on AWS Route53 but I’m still having issues

The domain I’m using is earnx.app

Looks correctly configured to me via our system:

https://app.netlify.com/sites/earnxapp/settings/domain#branch-subdomains

You could use the API calls you can see when you create one in the dashboard, following this recipe: [Common Issue] Understanding and using Netlify's API so you could automate in the future:

  1. commit on branch that your site is configured to build
  2. let the build complete successfully
  3. add the branch subdomain via API.