Can you share what you setup on the MX for this?

Any answer to this? i am also running into the same issue

Yes. I did put an ip in that field

when ipv4 is required, i am getting clients stuck in ip learn, but when off they get dhcp fine

i am not using SVI on the c9800, the ip helpers are on teh upstream core switches. when ipv4 is required, i am not getting clients stuck in ip learn, but when unchecked they get dhcp fine.