Seafile on Plesk does not work: ModuleNotFoundError: No module named 'captcha.fields'

Symptoms

• Trying to open Seafile results in an "Internal Server Error"
• The following error can be found under the domain log /var/www/vhosts/example.com/logs/seahub.log:

CONFIG_TEXT: [ERROR] django.request:135 handle_uncaught_exception Internal Server Error: /seafile
Traceback (most recent call last):
ModuleNotFoundError: No module named 'captcha.fields'

Cause

Bug in Seafile extension version 7.1.0-2, which should be fixed in the next update.

Resolution

As a workaround:

1. Connect to the Plesk server via SSH

2. Install the missing module for the Python library:

# pip3 install django-simple-captcha