Using a Wavlink AP

Have a LTE7490-M904 which works fine. I am now wanting to add a Wavlink AC600 wifi extender configured as an AP. I use an unmanaged switch which seems to work fine. Problem I cannot get the AC600 to access the interent. Have spoken to Wavlink who are useless. The AC600 works fine when connected to another network I have but not the Zyxel mobile phone one. Am I missing something obvious?