Rule reminder
In quanto has two functions: (1) as a causal conjunction meaning 'since / given that', introducing a clause with indicative — used in formal/written Italian; (2) as 'as / in the capacity of', indicating a role or quality. Example: 'Non posso votare in quanto straniero' (as a foreigner) vs 'Non ho risposto in quanto non avevo informazioni' (since I had no information).
Non ho potuto firmare il documento _____ non ero presente alla riunione.