I think it's important to keep in mind that giving in to emotional blackmail only reinforces the behavior and teaches the teenager that it's an effective way to get what they want. It's important for parents to stand firm and not give in while also being willing to listen and have open communication about the situation.
I think it's also worth noting that emotional blackmail can sometimes be a sign of deeper issues in the parent-child relationship, such as a lack of trust or unresolved conflicts. It's important to address these underlying issues in order to prevent emotional blackmail from becoming a recurring pattern.
On a related note, I recently came across an article on how to handle online blackmail and sextortion. It's a scary and unfortunately common issue in today's digital world, but there are steps you can take to protect yourself and seek help if you become a victim. The article can be found here: https://www.digitalforensics.com/sextortion