In translation projects and jobs you can select indirect clients and contact persons of indirect clients. It looks like this:

To select indirect client, click Expand () button near client drop-down control, to open modal dialog for selecting indirect client:

When indirect client is selected, then you will be able to send a copy of invoice created over such project or job, to an indirect client's contact person. This happens automatically, when you select an invoice and click send a message button:

In the result, indirect client's contact person will be added to the recipient list of a created message. After creating a message, you can then manually remove contacts whom you don't want to send an invoice.

Selection of indirect client in a project or job does not affect on payment balances with your clients (because main client still has to make a payment), but this field can be additionally used in your custom reports to get additional insights into work you perform.