Replaced POST with data

[KiOui]

Fixed an error where we consulted the POST attribute instead of data.

Closes #139

[JobDoesburg]

I think the CustomAutoSchema does not work properly, could you verify it?

The track id should show as a parameter and there should be example responses as well

[KiOui]

This is a POST parameter and therefor it should be specified within the POST parameters (and thus the request body). The parameters that are specified under "Parameters" in SwaggerUI can only be query, header, path and cookie parameters (and thus not POST parameters). See here for more details (under Parameter object).