"Two different lockfiles found" even though one of them doesn't exist anymore

[michaloslav]

I made some modifications to my repo and also transitioned from NPM to Yarn. I'm now trying to publish it but I keep getting the two lockfiles error.

I deleted the package-lock.json file, as instructed by the CLI but still got the same error. I tried adding a .slugignore file too, doesn't work either.

Here's exactly what I did:
delete the file from file explorer
git add -A
git commit -am "Removed package-lock.json"
git push heroku master -f

add heroku.slugignore to the root of the repo
git add -A
git commit -am "Added slugignore"
git push heroku master -f

Still the same error

[RasPhilCo]

This is a build error, not a CLI error. File a support ticket at https://heroku.support.