down (to sth)
to force sb to give you a definite promise or tell you exactly what they intend to do
SYN pin down :
She says she'll come, but I can't nail her down to a specific time.
NAIL SB
Meaning of NAIL SB in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005