I believe its simple not compatible with version 5.8.1 of WordPress.
On the old site it gives this payload:
{“headers”:{},”body”:”{\”message_id\”:5008504187727409789}”,”response”:{“code”:200,”message”:”OK”},”cookies”:[],”filename”:null,”http_response”:{“data”:null,”headers”:null,”status”:null}}
On the new one its this one:
{“headers”:{},”body”:”\n\n
We have an immense problem. Could you help to update it?