Does sending through SY guarantee that my invoices are legally compliant?

The tax compliance, in terms of the presence of required information, of invoices sent via the SY portal remains your full responsibility.

You undertake that all data extracted from the invoice, shown on the SY Portal and validated by yourself are present on the PDF invoice.

Additionally, as part of the implementation of the "audit trail" e-invoicing mode, you must implement documented checks to establish a reliable audit trail between the invoice and the delivery of goods or services.