Rsync: --verify shows an issue with dateutil

This is my first time setting up rsync. Seems to be an issue with the python script. When I go to save my rsync server information I get this message on the web interface:

“Connection to rsync host failed: Unknown error.Please check running 'management/ --verify 'from mailinabox sources to debug the issue.”

When I run python3 --verify I get this message:

Traceback (most recent call last):
File “mailinabox/management/”, line 11, in
import dateutil.parser, dateutil.relativedelta,
ModuleNotFoundError: No module named ‘dateutil’

As a longshot attempt to fix it I ran this:

pip install python-dateutil

No luck though. Still getting all the same problems. Am I do something wrong or does something else need adjusting?