2018 15" A1990 - Wont turn on after battery replacement

Recently completed all of the steps from this guide, using the toolkit and battery provided.

After charging and booting up, the battery icon was crossed out and didn't appear to be recognised correctly. Tried resetting the SMC but didn't change anything.

I noticed that the battery board data cable popped right out of the battery side connector without being unlocked while i was removing it from the logic board side (tbh i wasn't using much force at all, so not sure what happened). I thought this may have damaged the cable in the process and this was causing the issue above, so i ordered another cable online and replaced.

Now i cannot get it to boot (also no power to the trackpad, can't click) using the old or the new battery cable ribbon.

Nothing appears visibly damaged, so I fear something may have gone wrong beyond my meagre skills and my Macbook is now an expensive paperweight, but figured i would reach out to the experts here.

Are there are troubleshooting steps i can run through to pinpoint the issue?

Any ideas on what might have gone wrong, potential fixes?

Your help would be greatly appreciated.