Changelly gives you the message you need to post on the same page where they give you the address you need to send your NEMs. But be careful. When I first did it, I did not know about messages and I’ve just made something up. The second time, I accidentally ticked a little tickbox that encrypted the message.
My NEMs went through their NEM address but it had been 11 days and I am trying to get them to refund me my NEMs or proceed with converting them XRPs. Tried email, Facebook and tried to get their attention on Reddit. So far they have not done it. They said we’ve sent the task to our tech team. That was Thursday last week (25 May). Still not done.
It’s ridiculous. If the messages were so important to make or break a transaction, then there should have been more warning or pop ups because these errors I’ve done were so easy to make. Even then, the details of the transaction are visible on the block chain. I don’t get what their issue is if they return the funds back to the sender. They can see the sender address. I’m starting to think it’s a way to fleece people off. It may not be rational but when you’ve got thousands of dollars in NEMs sitting in their wallet and they have no reason to be keeping it for so long, you start thinking it is a possibility.
If you’re slightly unsure, don’t do it.