Can someone tell me what's the IP address of Singapore (ap-southeast-1) server?

Heya,

From what I understand, the ap-southeast-1 has multiple relay servers, this means there are multiple IP's but it's not really possible to know which one you were interfacing with.

Currently IP addresses of these relays are visible under: %userprofile%\Saved Games\Respawn\Apex\assets\temp\netcfg
The relevant IP's related to ap-southeast-1 seem to be those under sgp, which are:

103.10.124.116
103.10.124.117
103.10.124.118
103.10.124.119
103.10.124.120
103.10.124.121

Though I'm not 100% sure, so I'd recommend reading through the netcfg yourself, which is encoded in JSON.
(+ It's also possible the netcfg itself does not provide accurate data, though I'm assuming it does for now)