Entrepreneurial activity with ENISA
You develop in Spain an economic activity qualified as entrepreneurial under article 70 of Spain's Entrepreneurs Act (Law 14/2013). Requires a favourable ENISA report (Empresa Nacional de Innovación) certifying the innovative nature of the project.
It is the most structured route and the one that best withstands AEAT review — but requires additional ENISA processing before filing Form 149.