Drive API suddenly returning storageQuotaExceeded error, plenty of storage available

Please bear with me as I’m not super technically-inclined with Google’s cloud console and all its inner-workings.

I have a PHP script setup to take files and upload to a Drive account. It was working fine until April 23 when it suddenly started returning this storageQuotaExceeded error. I logged into the Drive account and there is plenty of storage available. Also, I’m able to manually upload files so I know there’s no actual storage issue.

What would cause this to suddenly start? I’m using a service account to access the API. The exact message is “The user’s Drive storage quota has been exceeded.”

I’ve found others online saying service accounts are limited to a separate 15GB storage quota but that can’t be the case here because the script was frequently uploading far more than that. Now that I’m thinking more about it, I suppose it’s possible this is the case. I have a server backing up to this account as well (with no issues) and it uses OAuth to login to the main Drive account so it’s not running into this quota issue. I guess I have to figure out how to incorporate that into this files script.