How is you DHCP and addressing set up?
[admin@MikroTik] > ip address print
Flags: X - disabled, I - invalid, D - dynamic
# ADDRESS NETWORK INTERFACE
0 D 192.168.10.17/20 192.168.0.0 WAN_1 PORT 1
1 D 192.168.10.75/20 192.168.0.0 PORT 2
2 192.168.10.1/20 192.168.0.0 PORT 2
I want to use Port 1 as a wan and take an external IP from my backend router use the Mikrotik as VPN SERVER!!!
# NAME INTERFACE DHCP-SERVER LOCAL-ADDRESS
0 relay1 LOCAL SWITCH 192.168.1.240 192.168.10.75
[admin@MikroTik] /ip cloud> print
enabled: yes
update-time: yes
public-address: 80.235.150.244
dns-name: lymperis.sytes.net
status: updated
warning: DDNS server received request from IP 80.235.150.244 but
your local IP was 192.168.10.75; DDNS service might not
work.