3557761 - Why are my Hungary invoices failing with NAV errors?

I'm sending a Hungarian invoice to my buyer and it is failing validations and throwing multiple errors such as:

ERROR: INV-662: You must provide your NAV registration information in your Ariba Network Company Profile to enable Ariba Network to report your invoices to the NAV.

ERROR: INV-555: You cannot create a tax invoice through SAP Business Network because you have not yet created a legal profile. Create and activate a legal profile first to ensure that the required invoice data is reported to the NAV (Company profile >> Additional Address >> Setup Legal Profile). However, if you want your invoices to be considered proforma, disable tax invoicing in your Company Profile >> Electronic Invoice Routing >> Tax Invoicing and Archiving.

ERROR: {INVOICE_NUMBER_NOT_UNIQUE=A megadott számla sorszámmal már történt adatszolgáltatás.}  

KBA , SBN-AN-TX-INV , Transaction (Invoicing) , How To