git, Heroku: pre-receive hook declined

Make sure you are pushing a repo that contains a proper supported app ( Rails, Django etc.) and you are not just pushing some random repo to test it out.

Newbie in Heroku: Error when push my app to Heroku

If that is not the case and you are pushing what you think is a valid app, contact Heroku support and they will fix it for you.

First, disable collectstatic:

heroku config:set DISABLE_COLLECTSTATIC=1

Then run:

git push heroku master

For more details and full steps, check here.

Deleting package-lock.json solved it for me

Make sure that you are using either npm or yarn.lock file-

Two different lockfiles found: package-lock.json and yarn.lock Both npm and yarn have created lockfiles for this application, but only one can be used to install dependencies.

After deleting yarn.lock and pushing the code again to git, my issue resolved.