Staging: invoice number

[ArcAnya]

When testing a fixed price contract on staging, because I wasn't sure if the invoice was sending, I sent a few in a row:

• the 2 first invoices (probably twice with "send" button) on that contract had the same invoice #
• the the 3 following invoices (probably with "send again" button) on that same contract had 3 different invoice #

@rickkdev 2 questions:

• My assumption would be that it should always be the same invoice number per contract & freelancer (no matter if fixed price or contest contract) do you know what would be correct here? Or is it just better to increment per default like that to make sure invoice nbs are always unique for the freelancer?
• What if the invoice info is not "usable" for any reason for the sponsor (for instance obvious fake name or else) - should there be an option like for the tax form for the invoice to be accepted before the freelancer can claim? (currently the freelancer can claim automatically once he sent the invoice)