20k/yr is a average salary for a junir developer in Spain. 30-35k/yr for an experienced one (5+ years). 35-45k for a manager.
The red flag for me is the lack of information about your role in the company. This means peope in HR don't have a clue about what is going on. Probably you'd be outsourced to a client (a sign of the non-negotiable money amount).