If you do git push heroku, you will see the following display. If you open the second line from the bottom here, you will see ** Method Not Allowed **.
The second line from the bottom of the above picture is a file for git, so let's open the URL after remote :.
If you open it without checking the link, it will be like this. Let's be careful (commandment)
This git link seems to be a git repository for deployment. It seems good to clone as a last resort if there is any problem. It seems that it should not be used as a legitimate "origin" repository. See the links below for more information.
When I open a git push URL on heroku, it says Method Not Allowed
Duplicate an existing Heroku application in Git (https://devcenter.heroku.com/ja/articles/git-clone-heroku-app)