I can share some insights regarding adding more than one logo in QuickBooks sales forms. Right now, adding more than one logo is currently unavailable in QuickBooks Online.
As a workaround, you might want to create a combined logo (Zapper and SnapSan's logo) and ensure it meets the necessary image requirements.
a .gif, .bmp, .png, .jpg, .jpe, or .jpeg file
smaller than 10 MB
24-bits or less in bit depth (or colour depth)
square-shaped, since rectangles don’t work
You can go through these articles to learn more about adding logos and customising sales forms in QuickBooks: