Laravel8 | Vuex: POST error 500 (Internal Server Error)

I’ve been learning Vue and Laravel for the last 2 months and recently I started to work on a project in order to apply all the knowledge I’ve learned so far. I set several GET and POST routes successfully but for some reason, this request keeps failing.
I’m trying to set a simple POST request using Vuex, Laravel and Axios but I keep on getting the 500 (Internal Server Error) and I’m not sure what is causing it. I have the feeling that it may be that the Model is not correctly set up, bcs if I output the data that the controller received, it looks correct but when I instantiate the model and save the data to DB I get the error.