Although I am not 100% certain this is the problem, there is a good chance your sequence is out of date.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Although I am not 100% certain this is the problem, there is a good chance your sequence is out of date.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