A customer abroad ordered and my SIM sent an international text. Can I stop texts to other countries?

Yes. Under Settings → Text messages, Texts to other countries, choose Only numbers in your own country and a text to a number that does not start with your restaurant's calling code is never handed to your phone, so it costs nothing; the page counts how many were held back that way in the last thirty days. WhatsApp is not affected, so a customer abroad still gets every WhatsApp message. Set your restaurant's country under Restaurant details first, or every number counts as at home. The SMS from your own SIM tab in the docs covers the switch.