Try and follow the below steps properly and i am sure you won't face any issue:
Southeast Asia (VNet-1)
Local Network in Southeast Asia
VPN IP (Temporary): 126.96.36.199 (Update this IP with your Gateway IP)
East Asia (VNet-2)
Local Network in East Asia
VPN IP (Temporary): 188.8.131.52 (Update this IP with your Gateway IP)
After this, go to the respective VNets and check Site-to-Site connectivity option, add the gateway subnet(if not added automatically) and from drop down select the opposite Local Network i.e. for Southeast Asia select EAsia Local and vice versa.
The error you're facing is because of IP Address range. You might have made a small mistake at some point.
Let me know if this works.