What Dynatrace are you on? Saas or Managed?
Did you open communication between components (Dynatrace Server or Env. AG if you are on Managed, Env. AG if you are on Saas)?
The communication flow is from Dynatrace component to vCenter (fqdn/ip) port 443
Did you create a user with correct view grants on vCenter?
If you need further troubleshooting than that you should first try the tips given by Dynatrace docs:
A lot of things can happen here, let us know!