*I am not able to create a subdomain in my droplet. It keeps saying *“Sorry! Something went wrong!”

Steps I followed, 1. I clicked on networking, 2. in my* domain.com box, I selected *more** and clicked on manage domain , 3. I selected CNAME , 4. in the hostname I put subdomain. (with dot), in the IS AN ALIAS OF, I added @

I am expecting to have something like: subdomain.domain.com
What is the issue? What can I do?