Write a simple API for example it can take a string input on a POST request and "store" this in a DB or in memory and then return said string when receiving a GET request. It should be possible to update the text with a PUT request.
It could also be a provisioning API, say you send in a POST request to create something with a status: on/off You can then read the status of this with a GET request. You can also change the status of this with a PUT request.
Try to have correct error codes. Write a short documentation on HOW to use your code and how to run it. What calls can be used to the API.
If you feel nice please limit your solution to: JavaScript, TypeScript, Python, Java (spring-boot) and C# 😃