a hook to add extra fee to invoice, is it possible?

[Metalik]

Hello

 

I need a hook to add extra fee to the invoice when domain name ordered contains "xn--" at the first.

 

I have read http://docs.whmcs.com/Hooks#Creating_a_Hook

 

Which hook point is used for this?

 

Are there any hook for download related to this?

 

Regards