YouTube Livechat API pageTokenInvalid

Well...I wanted to make a youtube live chat bot with controller.
I read this document: LiveChatMessages - Goggle developers
After reading this document, I make a link used with GET method for the program:[MY_API_KEY]
And they retrun an error:
"error": {
"code": 400,
"message": "page token is not valid.",
"errors": [
"message": "page token is not valid.",
"domain": "youtube.liveChat",
"reason": "pageTokenInvalid"

And then I tried the link without "&pageToken=CAUQAA", but still a same error returns.
Do anyone tried to make similar things?

Is my question too hard...

Do you have a valid API key? Look back at your parameters.

I daon't want to make it public