AC68U as access point to connect ip cam

Hi,

I am using AC87u as primary router and AC68u as access point in my new apartment.

I can connect to my IP cam (Foscam R2) via iphone app when the IP cam connected to primary router. But I have a problem that I cannot connect to my IP cam via iphone app when IP cam connected to access point.

In fact, I have less experience in using access point. What steps should I do to fix the problem?

Thank you.