I'm a programming novice, so I think it's a very simple problem, but I don't know the solution, so I'd like to know.
As the title says, I want to use oauth2client with heroku. When I actually deployed it and tried to operate it, the following error occurred in the log.

contents of log

2020-08-23T02:52:57.007580+00:00 heroku[web.1]: Starting process with command `python menta_ss_update.py`
2020-08-23T02:53:01.380834+00:00 app[web.1]: Traceback (most recent call last):
2020-08-23T02:53:01.380872+00:00 app[web.1]: File "module.py", line 11, in<module>
2020-08-23T02:53:01.380996+00:00 app[web.1]: from oauth2client.service_account import ServiceAccountCredentials
2020-08-23T02:53:01.381015+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/oauth2client/service_account.py", line 26, in<module>
2020-08-23T02:53:01.381128+00:00 app[web.1]: from oauth2client import crypt
2020-08-23T02:53:01.381129+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/oauth2client/crypt.py", line 23, in<module>
2020-08-23T02:53:01.381252+00:00 app[web.1]: from oauth2client import _pure_python_crypt
2020-08-23T02:53:01.381253+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/oauth2client/_pure_python_crypt.py", line 24, in<module>
2020-08-23T02:53:01.381378+00:00 app[web.1]: from pyasn1_modules.rfc2459 import Certificate
2020-08-23T02:53:01.381379+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/pyasn1_modules/rfc2459.py", line 23, in<module>
2020-08-23T02:53:01.381522+00:00 app[web.1]: from pyasn1.type import opentype
2020-08-23T02:53:01.381554+00:00 app[web.1]: ImportError: cannot import name'opentype'
2020-08-23T02:53:01.594072+00:00 heroku[web.1]: Process exited with status 1
2020-08-23T02:53:01.676492+00:00 heroku[web.1]: State changed from starting to crashed

I confirmed that there is oauth2client in requirements.txt, but I do not understand what is causing the error in this log.
version is as follows.


Please point out if there is a lack of information.