To change your invoice number, just tap on the invoice number when you're editing it.
You can add a prefix to all your invoice numbers, such as INV, or your initials. This is a global setting so will apply to all your invoices you create (but doesn't change previous invoices you've sent).
This is a number, and we add one to it each time you start a new invoice. Also, if you want to start where you left off in another system, or if you just don't want to start from a low number, you can change this to whatever you like and we'll start counting from there.
Sometimes, larger clients will give you a "Purchase Order" number that you have to include on your invoice, to help with their budgeting processes. You can add these here.
Check out this video to see it in action: