This was originally a question as I was getting an error.
After having downloaded the RestServices module, go to project settings -> runtime and change After startup microflow to a new microflow.
Add StartPublishServices to the microflow.
Add the service overview to your administration and compile.
Create two modules. One normal one and one for REST.
Create a domain model for both .
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Create a OnUpdate POST Service Microflow.
Run Mendix, add a new Published Service and enter the name of your microflow to run for your POST service.
Use postman to test the publishing POST Service.