When deciding on your visa application, the UKVI caseworker needs to be sure that you are a genuine student and that your intention is to come to the UK to study. They will test this by inviting you to a credibility interview via Microsoft Teams following an email invite from them. You MUST ensure that you attend the interview and you must not ask someone else to attend the interview on your behalf. The UKVI will refuse your application if you do not attend.
You need to be thoroughly prepared for the interview, as if you do not pass this stage then your visa will be refused. It is very difficult to overturn a credibility refusal, and normally Oxford Brookes University will not issue you with another CAS if you receive a refusal for credibility.