I refer to a lot of examples, but web hooks are not configured successfully, I do not know why? The URLs in the web hooks have also tried various situations, but they have always been 500 error.
Gitlab version : 10.6.2-ee
Jenkins version:2.83
Gitlab plugin: 1.5.4
Gitlab Hook plugin: 1.4.2
Error 500
means the server misbehaved.
You need to check the GitLab server logs to see the exact nature of the exception mentioned by the GitLab server.
It could be an authentication (token) issue, as reported in gitlab-ce issue 34143.
The OP blue mentions in the comments:
[...] because the GitLab and Jenkins services are not on a network segment.
There is also an open configuration "Allow requests to the local network from hooks and services"
That was mentioned in jenkinsci/gitlab-plugin issue 272
You have to enable "Allow requests to the local network from hooks and services" in Setting page in Gitlab with new updates.