For testing purposes I created a json-file db.json with no data like this:
{ "tasks": [ { } ] }

I also created a file routes.json
{ "/api/demo/tasks": "/tasks" }

I than started a json api server with json-server db.json on default port 3000

I changed 'url:' in api.js to url: 'http://127.0.0.1:3000' and ran vue-crud (simple-crud) by npn run serve
The vue-crud page displays with no errors. I add a record with the + symbol, the json-server accepts it with 201 and POST /api/demo/tasks 201 27.237 ms - 92. The db.json file got the record as expected:
{ "tasks": [ { "name": "test", "description": "this is a test record", "apiId": "demo", "id": 1 } ] }

The problem is, that vue-crud does not show this (or any) record. Refreshing does not help, the list stays beeing empty.