The first rule is not to panic or give in to threats. Many abusers play on fear and expect the victim to be frightened and rush to fulfill their demands. The second is not to engage in dialog and do not try to negotiate. If a person pays once, there is a high probability that the blackmail will continue. Another important point is to collect evidence: take screenshots of correspondence, save letters, record calls (if this is allowed in your country). This will help if the case goes to the police. It is also important to strengthen the protection of your data: use complex passwords, enable two-factor authentication, regularly check the privacy settings on social networks. You can read more about what to do if you are already being blackmailed in the article at https://azbigmedia.com/business/technology/victim-of-online-blackmail-here-is-what-you-need-to-do/ . There are useful tips on how to act correctly in such a situation

Fortunately, I haven't had such an experience, but I think it's important not to put on the internet something that can be used against you. And, of course, if the situation is serious, it is worth contacting specialists - lawyers or law enforcement agencies.