I built my own Docker image as suggested in #14.
Now I can use the REST API without the Internal Server Error.
However, there is a CORS issue.

When I tried an API call via Ajax request I got the following error:

Access to XMLHttpRequest at 'http://localhost:5000/tok/morph/pos/conv-morph/dep' from origin 'https://localhost:44399' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I can solve it with a new Docker build with modified uwsgi.ini.
I've added this line:

add-header = Access-Control-Allow-Origin: https://localhost:44399

Do you want to provide CORS support? Maybe in a configurable manner?