It is important to make sure that there are no non-deleted resources. Use the command mentioned in the following screenshot to list the available resources:
To view our volumes attached to running instances, we use the following command:
nova volume-list
If this is not the case, then we need to check the quota limits or increase if needed. Current quotas can be displayed using the following command:
nova-manage project quota admin
The number of instances can be increased using:
nova-manage project quota admin --key=instances --value=100