I got credentials from real account. So I can test more now.
Under dev account webhooks works perfect. I have access to few sites, I tried to send test webhooks to different sites on different servers. No problems, it works.
Under real account I tried to send the same test requests to different sites. It works for any site except my main site.
https://subdomain.my-main-site.com - not works.
https://my-main-site.com - not works.
https://my-second-site.com - works.
https://subdomain.my-main-site.com and https://my-main-site.com on server1
https://my-second-site.com - on server2.
I removed all api clients and webhooks records from dev account (I thought maybe it have issue with duplicated domains in 2 different accounts). The same result.
I have not messages when I create or delete webhooks. I enter URL, click + and see webhook below.
When I click “send test” I see popup. It show me correct url and button “send test”. I click to the button and nothing happens. Not errors, no window with result.