No internet on tp-link archer c20 v5

Hi all
I have just installed openwrt on archer c20 v5 but when i connect the wan port on this router to my ISP internet router, the wan interface doesn't show any activity nor any ip address associated it with it.
If i connect the ethernet cable coming from ISP router to my pc, I get an IP and internet. So there must be some configuration missing on the openwrt.

Can you please help me with getting it to work?

Try cloning the PCs MAC address onto the routers WAN port.