New instance can't upload images

I just got a new instance up and running (more or less) and am currently running into errors when I try and upload images SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data. I get two of these popping up in the lower right whenever I try and upload an image.

I found this GitHub post which ends up linking to this Stack Overflow post. I'm still pretty new to setting up servers, and the ones I have set up have all used Apache so this is very foreign to me.

Could I get some help troubleshooting if I'm actually running into the issues described in the linked posts or if I'm hitting something else? And if so, could I get help tracking down all the config files in the Lemmy install?