We are using ngrok to create the webhook endpoint.
**.ngrok.io resolves to ...
The certificate should be trusted by all major web browsers (all the correct intermediate certificates are installed).
The certificate was issued by DigiCert.
The certificate will expire in 246 days.
The hostname (****.ngrok.io) is correctly listed in the certificate.
Have you checked your SSL cert? If it expires communications stop.
More info from LINE Dev Thailand channel on YouTube (in Thai) https://www.youtube.com/watch?v=oxE4Ri_z__E
Change region of NGROK from USA (default) to Japan solved the problem.