In Size of Paper forum, what causes a thread to be locked?

They probably locked it because they didn't want anybody responding to it. They are strict at on that forum and they will deduct money from your account if you post duplicate discussion.They usually lock a post if they don't like the discussion for one reason or another ( if it breaks their rules) or if the discussion is a duplicate. I've decided to not be a member there anymore because they can be very rude about there precious rules being broken. I sent a private message to one of the moderators and asked them a friendly question about something and their response back was very unnecessarily rude and unfriendly. The forum is too strict and even though they pay well it's not worth my time if I'm constantly worried that my money is going to be deducted or they will ban me for some silly unknown reason. I like Mylot better. And If I feel the need to join another Pay per post site there are A LOT of them on the internet to chose from that pay.

Where exactly were you posting your threads? Most of the time your thread will be locked if it's a topic that has been discussed before. They are strict about this so you want to search before posting your topic. Also, if it is some kind of topic looking to solve a problem, they'll lock it once you get an answer. This will prevent others from spamming on the thread. If you're posting in the make money section, be sure you read the sticky announcement. They have a specific format to follow if you want to post about a gpt site. That's all I can think about at the moment.