If you ever happen to encounter a moment where you see 4G icon is available, signal bar is full but Voiceping unable to send or receive any messages as it shows "Cannot send message because ws is disconnected", here is how to solve it.
Please note that steps below might be different depends on device type, example below is using Voiceping Teams
1. Open phone settings
2. Go look for Network and Internet> Mobile Network > Access Point Names > choose the proper APN based on your carrier (ex, for Singtel, choose IDEAS)
3. Go back to Network and Internet Settings > SIM Cards > Make sure the preferred SIM for Mobile data is match with the sim you use for internet.
4. Go back again to Network and Internet Settings > Data Usage > Mobile Data > make sure this ON
After doing the steps above, you should now be able to see little 4G icon between the main big 4G icon and signal bar; meaning the internet is connected back.