503 Error on service bus message send from Logic Apps.

RunID: 08586362653094527714745890400CU34
Subscription: 0d440ec8-b273-4af9-b797-b209e72c0399

Raw outputs

{
    "statusCode": 503,
    "headers": {
        "Strict-Transport-Security": "max-age=31536000; includeSubDomains",
        "X-Content-Type-Options": "nosniff",
        "X-Frame-Options": "DENY",
        "Timing-Allow-Origin": "*",
        "x-ms-apihub-cached-response": "false",
        "Cache-Control": "no-store",
        "Date": "Fri, 09 Aug 2019 09:07:26 GMT",
        "Content-Length": "266",
        "Content-Type": "application/json"
    },
    "body": {
        "error": {
            "code": 503,
            "source": "logic-apis-westeurope.azure-apim.net",
            "clientRequestId": "94014b57-f71b-4695-b595-e41b5c26e5db",
            "message": "The response is not in a JSON format.",
            "innerError": "The service is unavailable."
        }
    }
}