OMG, muchisimas gracias! I've only encountered contracts recently in English and never in Spanish so I was having trouble trying to translate some of this legalese into Spanish! Thank you again, so much!It appears that you have a retainer agreement for legal services for pre-trial representation on a criminal matter.
In Spain, in this context and format, we would say:
Legal Fees: Honorarios Profesionales
Flat Fee: Retribución Fija (As compared to “periodica” o “por hora”.