There are three places to upload your logo in Billy
Main Logo Settings
Go to Settings > Organization
The dimensions for your logo are best optimized at 400 x 70 px
Just below your logo is the icon, this is the square people see in the corner of their browser in the customer portal:
The logo (Favicon) is 50 x 50 px
Your Invoice Template
The final place to upload you logo is in the invoice template. If you are seeing oversized logos in the customer portal or in pdf invoices, be sure to check this out.
Go to Settings > Templates > open the template you are using, probably default
Scroll until you see Alternative logo
This is also 400 x 70 px
The size of the image background for the invoices in the customer portal are:
900px x 1500+ px
Note that since invoice heights change based on the number of line items, it's not recommended to have a footer image and to keep the background height as large as possible to reduce duplication.