Insufficient capacity

That error occurs when the AWS infrastructure has insufficient capacity for the resources of the instance type being used.
If you encounter this error when starting an instance, you can temporarily work around the error by using one of the following methods.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/troubleshooting-launch.html#troubleshooting-launch-capacity

• Wait a few minutes and then submit your request again; capacity can shift frequently.
• Submit a new request with a reduced number of instances. For example, if you're making a single request to launch 15 instances, try making 3 requests for 5 instances, or 15 requests for 1 instance instead.
• If you're launching an instance, submit a new request without specifying an Availability Zone.
• If you're launching an instance, submit a new request using a different instance type (which you can resize at a later stage). For more information, see Change the instance type.
• If you are launching instances into a cluster placement group, you can get an insufficient capacity error. For more information, see Working with placement groups.

Other workarounds are possible by making on-demand reservations, but since you will be charged for the time you are not using the EC2, we recommend that you use the above method to solve this problem for testing EC2 and the like.
https://repost.aws/knowledge-center/ec2-insufficient-capacity-errors