If it already happened
It was not your fault. If it happened to you
Scammers are professionals at this; you were not. Whatever happened, money, photos, a meeting that went wrong, there are concrete steps that make it better, and people who will help without judging.
Keep everything
Messages, profiles, phone numbers, email addresses, payment receipts, the photos they sent you. Screenshots with dates. Do not delete the conversation, however much you want to: it is the evidence every report will need.
Report it where you met them
Every serious modelling site and social network has a report button. Use it, and describe what happened. It protects the next person, it starts a paper trail, and on a well-run platform it gets the scammer removed.
Report it to the police
Fraud, extortion with images and sexual coercion are crimes almost everywhere. Reporting is free, you can bring someone with you, and many police forces have online reporting for cybercrime. Bring your screenshots.
If images were shared, get them taken down
Report the images to the platforms where they appear; most have dedicated forms for intimate images shared without consent. Services such as StopNCII.org help prevent images from being spread further. You do not need to explain yourself to anyone to use them.
Tell someone you trust
A friend, a parent, a partner, a teacher, a helpline. You do not have to carry it alone, and you do not have to have all the answers before you talk. People who care about you will want to help.
Shame is exactly what a scammer counts on. Talking is how it loses its grip. None of this was your fault.