Are you using one of our examples for verifying the webhook? A 503 would be coming from your server which means that Square didn’t get the 2xx response within 10 seconds. Is a 503 also returned with test webhooks? 
Are you using one of our examples for verifying the webhook? A 503 would be coming from your server which means that Square didn’t get the 2xx response within 10 seconds. Is a 503 also returned with test webhooks?