Your invitation letter or your feedback may include reasons for asking you to a meeting, for example the marker may comment on incorrect sources or the writing style. If you do have some information about the marker's concerns, you can focus on those areas.
Gather any notes and drafts you can find, to show you worked on the assignment. You can send them to the Academic Conduct Officer (ACO) before the meeting or bring it with you if you're meeting in person. You may also still have the websites you visited in your browser history, which could show your research at the time of the assessment.
Go through your essay and remind yourself of the topic. Be prepared to answer specific questions about what you wrote - think of it as an oral exam where you explain your work. Think about the sources you used, how you found them, and why you decided to use them. Check for any incorrect references, and find the correct ones if there were any mistakes.
If your work is very different than your other assessments, did you approach it differently this time? Did you understand this topic more, put more effort into it, or have you worked hard to improve your skills?
If you did use AI to help you with your work, submit a statement to explain what happened. If there was anything happening in your personal life that was affecting your ability to study, make this clear in your statement and send evidence of those circumstances. Exceptional circumstances can change the penalty, so it's important the Academic Conduct Officer is aware of what happened.