Bulk assignment of ZTE Devices broken via CSV?

I have found a variety of these questions posted both here as well as across other places on the net.

It seems that the requirements to apply a bulk change to devices in ZTE are very specific. I cannot find a way to make it work. I’ve tried CSV files from Excel, Google Sheets, as well as just making it in a plain text editor.

Every single time the file is rejected as an unsupported file type. I would really like some clear guidance on how to make this work consistently if at all possible.

Thanks.