The following occurs when the number of fleets exceeds the service limits.

The following service limits were exceeded: <<Resource Name>>. Request a service limit increase from the service limits page in the console. 

You can find the service limits for your tenancy in the console. To check these limits, in the navigation menu, go to Governance & Administration, Tenancy Management, and click Limits, Quotas and Usage.

To avoid exceeding the limit, remove unwanted fleets and install keys before creating a fleet.

See Requesting a Service Limit Increase for more details.