Invoices
The register only issues receipts. It doesn't produce invoices in the customer's name and doesn't let you enter their company name, SIREN or VAT number.
The receipt does show your SIREN, SIRET and VAT number, along with the VAT breakdown. To give it to the customer, print it or send it by email from Receipts.
The Settings > Invoices page lists the invoices for your Vivlab subscription, not your customers' invoices.
Step by step: Issue an invoice instead of a receipt.