Can't create webhook subscription anymore [production]

Could it be possible that your server receiving the webhook is behind some firewall or in a private network?
You might be able to hit it since you are part of the same network
Could you try hitting the webhook from a public network just to be sure?
Also, make sure your webhook endpoint responds within 3 seconds when receiving a GET request so that RingCentral knows it's up and running

I've checked by 'https://portchecker.co' if my '6f48022e8fe2.sn.mynetname.net:3333' is accessible from external - the port is OPEN.

But I still have (without any incomming request):

com.ringcentral.RestException: HTTP Response

=============

status code: 400

Server: nginx

Date: Wed, 20 Apr 2022 12:38:45 GMT

Content-Type: application/json

Transfer-Encoding: chunked

Connection: keep-alive

LocalHostInfo: 10.120.28.93__17316@iad41-c01-csg13.c01.ringcentral.com

RCRequestId: cf597584-c0a6-11ec-8ca4-0050569c35a6

X-ERROR-ID: cf597584-c0a6-11ec-8ca4-0050569c35a6

X-Rate-Limit-Group: medium

X-Rate-Limit-Limit: 40

X-Rate-Limit-Remaining: 39

X-Rate-Limit-Window: 60

RoutingKey: IAD01P10

{"errorCode":"SUB-521","message":"WebHook is not reachable","errors":[{"errorCode":"SUB-521","message":"WebHook is not reachable"}]}

HTTP Request

============

HTTP POST https://platform.ringcentral.com/restapi/v1.0/subscription

Authorization: ??

X-User-Agent: RC-JAVA-SDK Java 1.8.0_221 Windows 2003

{"eventFilters":["/restapi/v1.0/glip/webhooks"],"deliveryMode":{"transportType":"WebHook","address":"https://6f48022e8fe2.sn.mynetname.net:3333/","encryption":true,"verificationToken":"******"},"expiresIn":63072000}

at com.ringcentral.RestClient.requestRaw(RestClient.java:316)

at com.ringcentral.RestClient.request(RestClient.java:328)

at com.ringcentral.RestClient.request(RestClient.java:257)

at com.ringcentral.RestClient.post(RestClient.java:148)

at com.ringcentral.paths.restapi.subscription.Index.post(Index.java:49)