Environment: python 3.6.6
learn the last chapter of "Python programming: from introduction to practice". After executing git push heroku master in a virtual environment, the following error occurs

(ll_env) D:\learning_log\ll_env\Scripts>git push heroku master
Counting objects: 79, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (73/73), done.
Writing objects: 100% (79/79), 6.38 MiB | 210.00 KiB/s, done.
Total 79 (delta 11), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Python app detected
remote:  !     The latest version of Python 3.6 is python-3.6.6 (you are using Python 3.6.6, which is unsupported).
remote:  !     We recommend upgrading by specifying the latest version (python-3.6.6).
remote:        Learn More: https://devcenter.heroku.com/articles/python-runtimes
remote: -----> Installing Python 3.6.6
remote:  !     Requested runtime (Python 3.6.6) is not available for this stack (heroku-16).
remote:  !     Aborting.  More info: https://devcenter.heroku.com/articles/python-support
remote:  !     Push rejected, failed to compile Python app.
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: !       Push rejected to salty-woodland-32065.
remote:
To https://git.heroku.com/salty-woodland-32065.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to "https://git.heroku.com/salty-woodland-32065.git"

so here"s the problem. I checked on the official website python-support" rel=" nofollow noreferrer "> heroku support Center ,

Supported Runtimes

python-3.7.0 on all (cedar-14, heroku-16, and heroku-18) runtime stacks
python-3.6.6 on all (cedar-14, heroku-16, and heroku-18) runtime stacks
python-2.7.15 only on cedar-14 and heroku-16 runtime stacks

and I also use python-3.6.6
how to break it? Ladies and gentlemen.