EC600N Network Radio Setup Help

I have ordered a network radio (Walkie Talkie) that uses the Quectel EC600N and have been trying to get it to connect to lte data.
I have set the APN using AT commands and it just won’t connect.

AT+QICSGP=1,1,“4gn.jp”,“roke@moba”,“rokemoba”,3

The SIM is a data-only one in Japan that we have previously used with Android-based devices.

I’m trying to connect to an APN name: 4gn.jp User: roke@moba Paswword: rokemoba Auth Type: PAP or CHAP

This seems to be the code that sets the APN but it will not connect to data. I’ve been trying various tutorials I have found online and it now won’t connect to the desired network at all and keeps returning *REJCAUSE:0,0,19
and various other errors. Also, when restarting the device it loses network connection.

The manufacturer is finding it difficult to find a solution for me and I want to see if I can find a solution myself before a refund becomes the only option.

Does anyone know where I can start in educating myself in getting these devices to connect to a data connection?

Any help will be greatly appreciated. I am very new to this type of device.