Sending an invoice to a liberal professional

I need to draw up an invoice for a liberal profession. This person is coming to me for training.
If I am not mistaken, they are not obliged to be able to receive invoices via Peppol.

When creating the invoice, should I select ‘private person’ under ‘customer’? Or should I choose ‘belgian company’ and not fill in a vAT number? When I fill in the company number, I get a notification saying that sending via Peppol is required.

Can these invoices be sent by email?

Thanks in advance!