no problem; it doesn't matter; I don't mind
Polite expression used to give permission, express indifference, or reassure someone that something is acceptable. Often used in response to a request or suggestion.
Do you mind if I sit here?
It's okay if you're late.
構いません is the polite (丁寧語) form of 構わない, used in formal speech to say 'I don't mind'.
Polite negative form of the verb 構う (かまう, 'to mind, to care about'). The phrase literally means 'I do not mind' and has become a fixed polite expression.