Error integrating Sentry with Ionic 4

I have inherited an Ionic 4 project, and wanted to add Sentry. I’ve added Sentry to Ionic 3 projects in the past no problem. However, when I go to build, I receive the following:

Sentry: build path does not exist C:\Users\Chris\{project name}\platforms\android\www
This is not an Ionic project, please check out:
to find out how to correctly upload sourcemaps for your project.

I’ve followed the documentation, including initial setup documentation here:

Not sure what I could have missed - any help appreciated.