unsuccessful apply

[eumoh1601]

no successful apply
i cannot successfully run an apply for my exercise. i keep having this error. And i am using the right AMI's from AWS.

error output:

Error: Error applying plan:

2 error(s) occurred:

• aws_instance.backend[0]: 1 error(s) occurred:

• aws_instance.backend.0: Error launching source instance: Unsupported: The requested configuration is currently not supported. Please check the documentation for supported configurations.

    status code: 400, request id: ebc26be4-f0f5-4d87-8398-9554736be0cd
  

• aws_instance.backend[1]: 1 error(s) occurred:

• aws_instance.backend.1: Error launching source instance: Unsupported: The requested configuration is currently not supported. Please check the documentation for supported configurations.

    status code: 400, request id: 805c6b76-57fc-4159-9ebb-e99ac6fb59ee