Manual remediation config works, automatic remediation config fails

SOLVED! There was a syntax problem in the runbook, that is not detected when manually remediating. In the content of the remediation doc (that was created using Cloudformation), I used a parameter declaration: parameters: InstanceID: type: 'AWS::EC2::Instance::Id'

It should be: parameters: InstanceID: type: String

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I have a remediation runbook that creates Cloudwatch alarms for the metric 'CPUUtilization' for any EC2 instances that have none defined. The runbook is configured as a remediation document for a config rule that checks for the absence of such alarms. When I configure the remediation on the rule as manual, all goes well. When I configure the remediation with the exact same runbook as automatic, the remediation fails with this error (snippet): "StepDetails": [ { "Name": "Initialization", "State": "FAILED", "ErrorMessage": "Invalid Automation document content for Create-CloudWatch-Alarm-EC2-CPUUtilization", "StartTime": "2022-05-09T17:30:02.361000+02:00", "StopTime": "2022-05-09T17:30:02.361000+02:00" } ],

This is the remediation configuration for the automatic remediation. The only difference with the manual remediation configuration is obviously the value for key "Automatic" being "false"

{

"RemediationConfigurations": [
    {
        "ConfigRuleName": "rul-ensure-cloudwatch-alarm-ec2-cpuutilization-exists",
        "TargetType": "SSM_DOCUMENT",
        "TargetId": "Create-CloudWatch-Alarm-EC2-CPUUtilization",
        "TargetVersion": "$DEFAULT",
        "Parameters": {
            "AutomationAssumeRole": {
                "StaticValue": {
                    "Values": [
                        "arn:aws:iam::123456789012:role/rol_ssm_full_access_to_cloudwatch"
                    ]
                }
            },
            "ComparisonOperator": {
                "StaticValue": {
                    "Values": [
                        "GreaterThanThreshold"
                    ]
                }
            },
            "InstanceID": {
                "ResourceValue": {
                    "Value": "RESOURCE_ID"
                }
            },
            "Period": {
                "StaticValue": {
                    "Values": [
                        "300"
                    ]
                }
            },
            "Statistic": {
                "StaticValue": {
                    "Values": [
                        "Average"
                    ]
                }
            },
            "Threshold": {
                "StaticValue": {
                    "Values": [
                        "10"
                    ]
                }
            }
        },
        "Automatic": true,
        "MaximumAutomaticAttempts": 5,
        "RetryAttemptSeconds": 60,
        "Arn": "arn:aws:config:eu-west-2:123456789012:remediation-configuration/rul-ensure-cloudwatch-alarm-ec2-cpuutilization-exists/5e3a81a7-fc55-4cbe-ad75-6b27be8da79a"
    }
]

}

The error message is rather cryptic, I can't find documentation on possible root causes. Any suggestions would be very welcome! Thanks!