Do I need to sign up for Liquid to pay an Invoice?

If you have received an Invoice from your Vendor, you can pay it with a Guest account (without creating an account) or with an Express account.

When paying an invoice this way, you'll be charged $3 per domestic invoice paid or $8 per international invoice paid. 

Later, if you decide to use Liquid's full capabilities, you can upgrade your account to a full Client account.