Allow Customer Signup on B2B Site
If you would like customers to be able to create their own B2B accounts, go to Admin -> Billing -> Company Options -> General -> B2B.
Check the box labeled Allow Customers to Sign Up On B2B Site. This will let customers create their own login accounts.
You can create a B2B customer account internally by going to Income -> Customers -> B2B Users.
There is not currently an option for vendors to create their own accounts. You will need to create these by going to Expenses -> Vendors -> B2B Users.