Thanks for your clarification! Much appreciated!

Yes, italki explains that this is a restriction in their list of Frequently Asked Questions. Each user is limited to three trial lessons. I think there is some confusion because most people assume the purpose is to "try" different teachers, and indeed, many teachers including me use it as such to see whether it's a good idea for us to work with a particular student. However, I believe the intention behind trial lessons is for users to "try" online lessons, at a rate that is typically reduced, before deciding if online language learning works for them. In any case, all lessons, including trials, require payment usually.