Trigger a build job when a repo folder is updated

Right now I have a repo in ADO that contains multiple microservices. I have build jobs that correlate to each of the folder. My question though is I am trying to make it if code is checked in to a specific folder in that repo to start the build job. What is the easiest way to do this. I’ve tried service hook but that only fires a job when it sees a repo updated not a folder.