Definition of it won't do in English:

it won't do

phrase

British
  • Used to express the speaker's opinion that someone's behavior is unsatisfactory and cannot be allowed to continue.

    ‘Don't talk like that—I've told you before, it won't do’
    • ‘I know that I am still recovering from fatigue, but I can use tiredness as an excuse and that just will not do.’
    • ‘It simply will not do for an elected government to fob people off with clichés and half truths.’