How to link a subdomain to a VPS if the main domain is on shared hosting?

Question

Domain Name System

Good afternoon.
There is a domain - example.com. It is tied to shared hosting. Managed via ISP panel.
There is a VPS on Digitalocean. The application is on the server. You need to bind the application to a subdomain - app.example.com.
What has already been done. I went to the ISP panel in the domain settings and added an A record there
'app.example.com.' and server IP on DO. But it doesn't work.
What have I done wrong?

Answer 1

$ dig +short app.example.com @shared_server
Check if the IP is given from the shared server itself.
Also, look at how many ns the zone is given: $ dig +
trace app.example.com
$ dig +trace example.com to NSs.