gitlab to jenkins job webhook test failing with 404

Hi Team , I am facing issue for created webhooks ( gitlab to jenkins job) testing .

Gitlab version : Gitlab Community Edition 12.2.5 Jenkins version : 2.204.1 Gitlab Plugin :1.5.13

Steps to replicated:

1. Jenkins user creation and its API token . and provided the user rights to build/configure the jenkins job .
2. Jenkins and gitlab connection established ( managed jenkins >> configure system ) Test connection result success . Enabled authentication for /project end point : checked/unchecked and tried in both scenario.
3. go to project in gitlab ( project >> integration ) and then entering https:jenkinsuser:API token@jenkinsserver/project/$JOB_NAME
4. Add webhook & test and I am getting below error. " Hook executed successfully but returned HTTP 404 default backend 404"
5. in request/response details response body : default backend 404

Please suggest