Hi @Rick Elder ,
Please use following param for configuration assignment.
Following is correct command
Arc resource (HybridCompute)
az maintenance assignment create --resource-group AWSUpdateMgmt --location eastus --resource-name i-0abd518c9631e9c52 --resource-type machines --provider-name Microsoft.HybridCompute --configuration-assignment-name PatchingConfig --maintenance-configuration-id "/subscriptions/a7d40ff7-d9ce-4b80-916e-d0c6c7bb657d/resourcegroups/AWSUpdateMgmt/providers/Microsoft.Maintenance/maintenanceConfigurations/Playground-WeeklyPatching"
Azure VM.
az maintenance assignment create --resource-group RGName --location eastus --resource-name --resource-type virtualmachines --provider-name Microsoft.Compute --configuration-assignment-name PatchingConfig --maintenance-configuration-id <mrpconfigurationarmId>"