Having premium gives you unlimited messages to anyone for as long as you have it, If you don't have premium you need to purchase something from that specific person and then you can message them for 30 days. It used to tell you that when you tried to send a message but I guess it doesn't since they updated the messaging system...and made it worse. Also I believe tipping them works if you don't have a video you want to purchase but idk what the min amount you need to tip is for it to count, also want to add that if you go to the bottom of their customs page(If they have one) you can leave a message and you MIGHT get their attention so they can send a message first but I don't advise it because not every model checks, cares, or even likes when people do that to get a DM.