Hi
I tested with www.mail-tester.com and they reported that the invoice email is being down scored by -0.5 simply because there is an image without an alt tag.
Can you consider maybe adding one when you get a chance please, just to aid delivery a little 
Thanks Hillel, and Happy New Year.
See below for report…
We found 1 images without alt attribute in your message body -0.5ALT attributes provide a textual alternative to your images.
It is a useful fallback for people suffering from sight problems and for cases where your images cannot be displayed.<img src="data:image/png;base64,iVBORw0KGgo....If you don’t want to add an alt attribute, add an empty one: alt=""