Fullstack Ruby on Rails Developer to fix a deployment bug

I have an app hosted in Heroku, and I'm having a deployment issue.
The app works great in development, but fails to compile when pushed to Heroku.

Stack used:
ruby 2.6.6
rails 6
webpacker
tailwindcss v2
postcss-loader

This is a partial of the errors I get:
ERROR in ./app/javascript/stylesheets/custom.scss
Module build failed (from ./node_modules/mini-css-extract-plugin/dist/loader.js):
ModuleBuildError: Module build failed (from ./node_modules/postcss-loader/src/index.js):
Error: PostCSS plugin postcss-purgecss requires PostCSS 8.
Migration guide for end-users:
https://github.com/postcss/postcss/wiki/PostCSS-8-for-end-users
at Processor.normalize (/Users/path/node_modules/postcss/lib/processor.js:167:15)
at new Processor (/Users/path/node_modules/postcss/lib/processor.js:56:25)
at postcss (/Users/path/node_modules/postcss/lib/postcss.js:55:10)
at /Users/path/node_modules/postcss-loader/src/index.js:140:12
at /Users/path/node_modules/webpack/lib/NormalModule.js:316:20
at /Users/path/node_modules/loader-runner/lib/LoaderRunner.js:367:11
at /Users/path/node_modules/loader-runner/lib/LoaderRunner.js:233:18
at context.callback (/Users/path/node_modules/loader-runner/lib/LoaderRunner.js:111:13)
at /Users/path/node_modules/postcss-loader/src/index.js:208:9
@ ./app/javascript/packs/application.js 7:35-65