nail down

informal
to make someone give you exact details or a firm decision about something:
They nailed him down to a specific time and place.
(Cambridge Advanced Learner's Dictionary & Thesaurus からの nail sb down の定義 © Cambridge University Press)

ビジネス英語
to make someone give you exact details or a firm decision about something:
nail sb down on sth
We've been trying to nail them down on the specific points of the agreement for the past six months.

nail sb down to sth
Things are getting urgent so we need to nail them down to a delivery date.
(Cambridge ビジネス英語辞典 からの nail sb down の定義 © Cambridge University Press)

- Cambridge Dictionary