Heroku App crashing from missing 'request-promise' Module
try npm i request-promise or npm install request-promise -s so it will save request-promise in your package.json. Then try to deploy
you are very close; but it seems that you left your request-promise inside the devDependencies by accident. Request-promise should be in the dependency because it is a package that you need for your application to work. To clarify, packages under devDependencies will be removed before deployment
Bahram is right, you need to do npm install request-promise. You probably did npm install request-promise --save-dev and as a result, it saved it under your devDependencies
Best to keep your devDependencies and dependencies separate. You may find this Heroku doc helpful => https://devcenter.heroku.com/changelog-items/1376