django.db.utils.IntegrityError: duplicate key value violates unique constraint "django_content_type_pkey"

Although I am not 100% certain this is the problem, there is a good chance your sequence is out of date.

Does executing this within Postgres solve the issue?

SELECT setval('django_content_type_id_seq', (SELECT MAX(id) FROM django_content_type));

This usually means that your primary key sequence has gone out of sync. This may have been caused by a bad migration etc..
To fix this;
1. Start the dbshell
python manage.py dbshell
2. Find the current highest value of the primary key
select max(id) from django_content_type;
3. Change the primary key sequence to now start at a value higher than the value found in step 2.
So assuming the value returned in step 2 was 290780 then alter sequence to start at a number greater than 290780
alter sequence django_content_type_id_seq restart with 295000;