How is IRPF handled when an invoice is made by a freelancer or a small company in Spain

I have a great experience in accounting and also a programmer specialized in accounting programs I read your description of what you want You are talking about The IRPF (Spain's Income Tax) for freelancers and you want to understand how it works And how to add that feature to the program Correctly Perhaps through my accounting and software experience I can help you achieve your goals and Through the discussion, we can decide together the best way to add this feature to your program