You are trying to update Greeting Text, but it is not changing or is not visible in the chat box on Facebook before the conversation with the Page is started. The issue is caused by the First Name variable and the lack of characters left to use in the Greeting Text while you're trying to set it up in your ManyChat account and save it. For example, if there are 4 characters left in the Greeting Text and there's a First Name variable in it, user named Bill will see the Greeting Text, but Jonathan won't see it - obviously, because his name is longer.
How to troubleshoot?
In this situation, we recommend deleting First Name variable from the Greeting Text - save it then and check if it works properly. If you'd like to leave the First Name variable in the Greeting Text, it is recommended to make the text 10-15 characters shorter, as the variable itself consists of 14 characters, plus it all depends on the length of the user's name.
Hope this helps!