IAM:PassRole is often one I see missed that leads to this error: https://docs.aws.amazon.com/autoscaling/ec2/userguide/ec2-auto-scaling-launch-template-permissions.html
You can also check cloudtrail for a RunInstances call made at the same time as the failed API, which might have more details on what permission was missing. If there's an encoded error, you'll need to use the
sts decode API to see the reasons
The error "You are not authorized to use this template" when updating your Auto Scaling Group (ASG) with a launch template can be due to insufficient IAM permissions. To resolve this issue, you should ensure that the IAM credentials you are using have the necessary permissions to perform the required EC2 API actions, including the ec2:RunInstances action. Additionally, if your launch template specifies any tags, you must also have permission to use the ec2:CreateTags action
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ok. Might be possible. However, just found that in my case it was restrictions imposed by my organization team that the base image cannot by a custom AMI. It has to be one of the standard AMIs.