I get this error with the mod enabled:

https://i.imgur.com/KzxhRr8.png

If there's a quick fix I could apply on my own, that'd be great, otherwise I'll wait on an update I guess :P

Hi. I can't reproduce that error in the mod loadouts I've tried. Do you have any mods that might be modifying chemical plant (or even basic chemical plant) in some way?

Since I can't reproduce, I don't have a guaranteed quick fix, but removing the next_upgrade might fix it:
https://github.com/brevven/bzgas/blob/7c766d2ab4d988518afbceb88ca462b744823b9f/prototypes/basic-chemical-plant.lua#L58

Hello. Apologies, I have initially tried enabling this with a couple of mods, the main one being SeaTorio (https://mods.factorio.com/mod/SeaTorio), which does add changes to the chemical plant. I have also misread the required mods section on SeaTorio's page before writing the previous message, clearly SeaTorio doesn't need the entire Very BZ mod pack, but rather just a couple of things from it.

Thanks you for the quick response and the suggestion, though, as this might still be helpful when I inevitably go overboard with mods and need to solve minor incompatibilities between them.