I am trying to install FFMPEG to work with my NodeJs server.
I am using heroku-buildpack-multi
plugin:
heroku config:set BUILDPACK_URL=https://github
I just tried this with a demo app I cloned from Heroku:
https://github.com/heroku/node-js-getting-started.git
I was able to deploy successfully following the same steps you listed above, except I added an 's' to the end of your second buildpack (you have a typo - could this be the issue?): https://github.com/heroku/heroku-buildpack-nodejs
I would recommend following the same process with a fresh codebase to help troubleshoot your environment. But note two things: 1) The heroku-buildpack-multi plugin you're using is deprecated, and 2) Heroku officially supports multiple buildpacks:
https://devcenter.heroku.com/articles/using-multiple-buildpacks-for-an-app
and has an officially supported ffmpeg buidback you can use:
https://elements.heroku.com/buildpacks/jonathanong/heroku-buildpack-ffmpeg-latest