Merchants have a new "new invoice" option:
{F376999}
This leads to selecting a user and account, and then you can generate the invoice (only one actual "purchase" / line item for the moment). You can add a longer-form remarkup description to contextualize the billable items:
{F377001}
This sends the invoice and takes you to the merchant order overview screen:
{F377002}
For now, you copy/paste that link into a nice personal enterprisey business-to-business email; the recipient sees this:
{F377003}