no problem; it doesn't matter; I don't mind
Used to express that something is acceptable, not a concern, or that the speaker has no objection. Often used in response to a suggestion or to give permission.
See also: 構う
It's okay if you're late.
It doesn't matter which one you choose.
差し支えない is a more formal, written-style way of saying 'it doesn't matter', while 構わない is the everyday spoken equivalent.
構わない politely says 'I don't mind' or 'it's fine', while どうでもいい can sound more dismissive, implying total indifference.
だめ means 'not okay/no good', directly opposing 構わない's meaning of 'it's fine, no problem'.
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'.
構う is the affirmative base verb meaning 'to mind/care about', while 構わない is its negative form used as a fixed phrase meaning 'it doesn't matter'.
Negative form of the verb 構う (かまう, 'to mind, to care about'). The expression 構わない literally means 'does not mind' and has become a common phrase for expressing that something is acceptable or not a problem.