@EvilC 

Hi， Normally remote host cannot access the printer since they are not in the same network, in order to achieve it, you might need to open related ports on the router for your printer, please contact the printer support to confirm which ports need to open on the router for remote printing.

Then please refer to the instruction below to open the ports on the MR200:

https://www.tp-link.com/en/support/faq/1675/

Note: please check the Internet IPv4 address on Advanced->Status->Internet part to confirm if it is a private IP address or public IP address, if it is private IP address, it means there is another NAT in the front(if you are using SIM card for internet access, the another NAT is on your ISP side), in that case, the port forwarding will not work, you will need to contact your ISP to see if they could assign you a public IP address.