Application error (500)
AttributeError: type object 'datetime.datetime' has no attribute 'datetime'
Traceback

File /app/.heroku/python/lib/python3.10/site-packages/otree/mturk_client.py, line 43, in call_api+
File /app/.heroku/python/lib/python3.10/site-packages/otree/mturk_client.py, line 167, in create_hit+
File /app/.heroku/python/lib/python3.10/site-packages/otree/views/mturk.py, line 133, in post+
File /app/.heroku/python/lib/python3.10/site-packages/otree/views/cbv.py, line 65, in inner_dispatch+
File /app/.heroku/python/lib/python3.10/site-packages/otree/views/cbv.py, line 152, in inner_dispatch+
File .heroku/python/lib/python3.10/concurrent/futures/thread.py, line 58, in run‒
55.             return

56.

57.         try:

58.             result = self.fn(*self.args, **self.kwargs)

59.         except BaseException as exc:

60.             self.future.set_exception(exc)

61.             # Break a reference cycle with the exception 'exc'

self    None
File /app/.heroku/python/lib/python3.10/site-packages/starlette/concurrency.py, line 40, in run_in_threadpool+
File /app/.heroku/python/lib/python3.10/site-packages/otree/views/cbv.py, line 45, in dispatch+
File /app/.heroku/python/lib/python3.10/site-packages/starlette/routing.py, line 243, in handle+
File /app/.heroku/python/lib/python3.10/site-packages/starlette/routing.py, line 582, in __call__+
File /app/.heroku/python/lib/python3.10/site-packages/otree/patch.py, line 29, in __call__+
File /app/.heroku/python/lib/python3.10/site-packages/otree/patch.py, line 41, in __call__+
File /app/.heroku/python/lib/python3.10/site-packages/starlette/middleware/sessions.py, line 75, in __call__+
File /app/.heroku/python/lib/python3.10/site-packages/starlette/middleware/base.py, line 38, in coro+
File /app/.heroku/python/lib/python3.10/site-packages/starlette/middleware/base.py, line 45, in call_next+
File /app/.heroku/python/lib/python3.10/site-packages/otree/middleware.py, line 42, in dispatch+
File /app/.heroku/python/lib/python3.10/site-packages/starlette/middleware/base.py, line 25, in __call__+
File /app/.heroku/python/lib/python3.10/site-packages/otree/errorpage.py, line 227, in __call__

Ok, this error seems to be an error associated with otree version 5.11.0b2. 

I have caught that I was accidentally in a beta version, and now it works again.