Thanks for your question. Could you please specify the reason why our Invoice addon is not allowed to be used in Portugal? Unfortunately, we did not test any third-party service for generating the invoices about reservations made with our Hotel Booking plugin. So we can not recommend any service you mentioned.
in Portugal you are only allowed to make invoices with systems approved by the Portugese Tax office. This to assure that the invoicing process and required data (new invoices, credit invoices, etc.) is according to portugese law.