Responding to apologies — how to respond to apologies

That's OK and That's all right say that the situation is acceptable. It's fine, really also reassures the person. In everyday conversation, these responses are often enough on their own.

That's is short for That is. In writing, an apostrophe is required. OK and okay are two common spellings, but in the set expression the whole expression matters, not just the word OK.

Don't worry about it literally asks the person not to worry about the situation. After don't, use the base form worry, and introduce the specific problem with about.

The shorter Don't worry is also possible when the context makes the subject clear. Don't worry for it is unnatural in this meaning: the preposition about is required.

No problem describes the situation as one that does not create a problem. Never mind shows that the matter is not important enough to keep worrying about. It doesn't matter directly says that it is not important.

Never mind is a set expression without to. In It doesn't matter, the base form matter is required after doesn't. These phrases have similar functions, but the specific following reply may make one of them more natural.

Accepting an apology does not mean that you must always ignore the problem. You can first calmly reply That's OK or No problem, and then ask for a specific action: Please send the right file or Please close the window.

If the situation is genuinely not fine, you should not insincerely say No problem. At A2 level, it is enough to acknowledge the apology neutrally and name the needed action: Thanks for telling me. Please call the office now.

Yes and OK can be grammatically correct as separate replies, but after an apology they do not always clearly show that you are reassuring the person. That is why, in an exercise requiring you to “accept the apology and reassure the person,” a bare Yes would be outside the aim of the exercise, not a grammatical mistake.

You're welcome typically responds to thanks, rather than accepting an apology. I'm sorry too is appropriate only when both people have something to apologize for. You should assess the role of the reply in the specific dialogue, rather than declaring any other phrase grammatically wrong.

For a natural response, take three steps: understand what the person is apologizing for; decide whether you can genuinely put the problem aside; give a short reaction and, if necessary, add a reason or the next action.

You do not need to repeat the same expression in every situation. Never mind works for a small mistake, No problem for a delay, and when a correction is needed, use That's OK, but please…. Your own or invented situations are equally suitable for practice.