Connect R7000P to MR1100

[AML1618]

So Frustrating.

R7000P as wireless router to my mobiles,  and computers
R7000P as Wired Router,  through Netgear switched,  to Printer and NAS Storage.
Works 100%,  is Great.

I am connected to the internet through a (Telstra provided) MR1100,  which in and of itself works fine.

How do I connect R7000P to internet through MR1100 ?  I cannot get it to work reliably.
I am using an ethernet cable to join the two devices.

[additude]

Have you tried taking a verified good ethernet cable from the MR1100 to the WAN port on the Router then go into the router settings/config for the WAN section and set it up as DHCP?

Reboot.