Curl command not working properly

I am using GitLab Community Edition 8.14.3 2f0065b2. I trying to add the members via curl command into either project or group. But Its is not working properly.

For example, If I use --request POST --header "PRIVATE-TOKEN:xxxxxxxxxxxx" --data "user_id=604&access_level=30" "https://gitlab.company.com/api/v3/groups/625/members" command means, As per your document I will get the developer access for the user. But I got the guest access for him. I tried the same in projects also. But there too I facing same issue.

Is my curl command correct? or GitLab facing any issue regarding this?

The document I referred is https://docs.gitlab.com/ce/api/members.html#add-a-member-to-a-group-or-project