Startup Overseas Forums

We own two villas in the Algarve that we currently rent to an tourist organization who in turn lets them to holidaymakers. The company has stopped paying the rent to us until we issue them proper invoices showing the tax that has to be stopped at source - (nobody seems to know the exact percentage) So my question is can somebody please show me a template I can use not only showing the correct percentage but also what other relevant information is required on an Invoice.