I can't get a new Goldshell LT5 to work on the pool. It says the pool is invalid. I can get it to work on other pools. Have you looked at the LT5 compatibility on the pool?
It seems unlikely that this is a compatibility issue, since connection and authentication are quite straightforward in the Stratum protocol.
If it says that the pool is invalid and does not connect at all, chances are that there is a mistake somewhere in the connection details (URL, username, and password). Make sure that you are using the username and password of one of your workers as defined in your pool account, keeping in mind that they are both case-sensitive. Feel free to send support an email with screenshots of the miner's configuration page if you'd like us to double-check.