I've successfully set everything in the setting.py and when running py manage.py compress it runs without errors and I see that 2 blocks have been compressed.
Here is the template:
{% compress css %}
<link rel="stylesheet" type="text/css" href="{%static 'project/main.css' %}">
{% endcompress %}
When opening the site from the browser I see something happened (the filename changed to output.6a62b0ce8790.css and the Accept-Encoding: gzip, deflate is also shows up). However the filesize is not changing.
COMPRESSION_ENABLED = True is set and I also use DEBUG = True (I don't know if it matters).