Mikrotik To Fortigate IPSEC

Hello Everyone,

I have successfully setup site to site IPSEC between Fortigate and Mikrotik in our branches.
I can ping Mikrotik lan interface from the FortiGate side but not the devices in the other branch.The issue is when I go to Mikrotik there is no any static route to the FortiGate, even if I try to do this manually I can not see new interface added by IPsec configuration. So I don’t know how to add the static route.
The second question is, during IPSec configuration on Mikrotik wherever I want to fill the IP address of FortiGate it will accept only IP address no domain name but unfortunately I don’t have static IP address in the FortiGate side and I am using DYNDNS.

Thanks for any help