How to get notification from custom Groovy/NodeJs service through Gitlab before deployment in Preprod or Prod env

Hello. Recently I have started to move the CI-CD process of my project to GitLab. Here, we have a requirement.
Suppose, we have to deploy our build through Git pipeline in 3 environments i.e. DevEnv, PreProdEnv, and ProdEnv. Once, the merge request is completed and code is successfully merged, the build should be deployed properly in DevEnv without any outer intervention. But, if developer wants to deploy the same build in PreProd or Prod Env, the Git pipeline should first call a Groovy or NodeJs service that will send a notification to concerned project manager. If project manager approves it by triggering another Groovy or NodeJs service, then this service should trigger the Git pipeline to deploy the build in PreProd or Prod Env.

I searched in GitLab doc and found the use of API to trigger restful services in .gitlab-ci.yml file but not able to get how to use the response of that service to halt or resume or continue the Git pipeline process.

Thanks in advance for any support here.