Unable to see sonarqube results in gitlab by using gitlab plugin

Using Sonarqube 6.7 version (with sonar-scanner), gitlab plugin 3.0.2

I am trying to integrate sonarqube analysis report in gitlab as inline comments.

Sonar-project.properties file looks like this:

sonar.projectKey=<project_key>
sonar.projectName=<project_name>

sonar.analysis.mode=preview

sonar.sources=<source_folder>

sonar.sourceEncoding=UTF-8

sonar.language=c

sonar.cfamily.build-wrapper-output=<folder_name>

sonar.branch.name=<branch_name>
sonar.gitlab.commit_sha=<commit_sha>
sonar.gitlab.project_id=<project_id>
sonar.gitlab.url=<gitlab_url>
sonar.gitlab.user_token=<user_token>

Build is successful. But I see the below line in the log and I see no inline comments in gitlab.

DEBUG: ‘GitLab Commit Issue Publisher’ skipped because one of the required properties is missing

And also a new job is created in the end and it says Sonarqube analysis in progress and the job status is pending and it never starts.

Have you tried this ?

sonar.gitlab.commit_sha=$COMMIT_SHA 
sonar.gitlab.ref_name=$COMMIT_REF_NAME 
sonar.gitlab.project_id=$PROJECT_ID 
sonar.gitlab.unique_issue_per_inline=true