Invalid path in lifecycle script

I'm trying to replace the version number in one of my project's file at the postbump lifecycle script:

"scripts": {
  "postbump": "sed -i -r 's/(<span id=\"app-version\">)[^<]*(<\\/span>)/\\1$npm_package_version\\2/' app/views/footer.scala.html && git add app/views/footer.scala.html"
}

I tested the command beforehand and it works, but when I run it in the lifecycle, I get

The specified path is invalid.

I know the specified path is actually valid, so the problem must be elsewhere.