subscriptions.template.json

{
    "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
      "ApimServiceName": {
        "type": "string"
      }
    },
    "resources": [
        {
            "type": "Microsoft.ApiManagement/service/subscriptions",
            "name": "[concat(parameters('ApimServiceName'), '/53c765632095310385070001')]",
            "apiVersion": "2018-01-01",
            "scale": null,
            "properties": {
                "userId": "[resourceId('Microsoft.ApiManagement/service/users', parameters('ApimServiceName'), 'john-doe-contoso-com')]",
                "productId": "[resourceId('Microsoft.ApiManagement/service/products', parameters('ApimServiceName'), 'starter')]",
                "displayName": "Starter product subscription",
                "state": "active"
            }
        }
    ]
}