Hello maddoglee,

At the moment XLSM is not added as an acceptable file type for attachments in QuickBooks Online. Currently, these are the file type accepted are the following below, and we're unable to override the system as it is working by design.

• PDF
• JPEG
• PNG
• DOC
• XLSX
• CSV
• TIFF
• GIF
• XML

I understand your frustration with this process and the feeling that the current setup doesn't match your specific business need.  I can definitely add this to our customer feedback/suggestions and let our Product Team know. I'd recommend also you share your feedback through the Gear Icon and select Feedback in your QuickBooks Online account. 

Post again in the Community if you need more help with QuickBooks Online. I'll be around to assist you.