Best excuse?

So I have an event this week but something came up that I have to work. I literally cannot miss work because I really need the money, but the people running the event say that it’s unacceptable to miss it due to work. I’m trying to think of an excuse to use but I’m just scared that the person might offer to stop by my house to drop something off the day of. Does anyone have a better excuse to use? I literally become paranoid when it comes to lying and don’t want to, but I’m super intimidated by these people and being honest could put me in a bad place. Help a girl out lol

The event isn’t “mandatory” it’s just recommended to attend but they try to make it a priority. It was basically assumed that I was going in the first place. Plus I’d have to pay to go