C# code in Unity to call API to start all backend process flow from logging in to Flexmatch

Hi, Would really appreciate someone's help with this as I'm not a developer and have taken it upon myself to setup all the AWS infrastructure for a BR game in Unity-Gamelift. I have created various lambda functions having watched hours of videos for logging in a player to starting a game session and have set up matchmaking functions. The sticking point is I don't know how to start it all off in Unity when a user clicks on the login button to authenticate using API and lambda function to then start the matchmaking process. The various videos I've seen don't go into the Unity code for this. Any pointers would be great! :-)

Thanks,

Bhav