Tosca's Rest API: What configuration is needed to execute Change and Create commands?

I've configured Tosca's REST API. All the endpoints are available. All read commands are executed successfully.

However, when trying to Post changes to an object or trying to execute a task to create a new object (regardless of type), the API returns with a 500 - Changes are not allowed to this object and 404 - Task not applicable error. Spelling errors would result in a 404 - Task not found error, so that can't be it. When providing a wrong object ID the API will also return a different error.

Also, I'm unable to change the checkout state of on object. The API returns the Request with a 200 - success message. However, the changes aren't propagated. Neither in the front-end, nor when reading the objects with the API.

I'm authenticated with an admin user. Is there some config that I've missed?

When trying to change an object I use the following POST endpoint:http://ServerIP/Rest/ToscaCommander/$MyWorkspace/objectProviding the following payload:

{"Attributes": ["Name": "Name""Value": "SomeNewName"   ],"UniqueId": "$objectID"}

When trying to create an object I use e.g. the following GET endpoint:http://ServerIP/Rest/ToscaCommander/$MyWorkspace/object/$objectID/task/CreateTestCase

For the checkout I use the following GET endpoint:http://ServerIP/Rest/ToscaCommander/$MyWorkspace/object/$objectID/task/Checkout (only successfull request)

Both the endpoints and the payload appear to be syntactically correct. Therefore, I assume that I missed some magical "readOnlyEnabled=False" config setting. Since the error messages only contain the code a one liner, I don't know what the issue is.