Pete Daoust
I would send a Notice of Claim, before the invoice...
Notifying them my intent to CLAIM, and WHY I will claim. That way, they will have the opportunity to tell me WHY I shouldn't claim if they want....
And then, after 3 or whatever the amount of days I decide, I will send an invoice, unless they've explained to me on WHY I shouldn't claim :)
But that's just me :D