REG99 "Unable to connect"

I've had several Samsungs, LG, motorola, and every phone I've owned including my newest does either the reg 99, forbidden, or some other error code and it happens daily. Here's the best fix I found:

Toggle Wi-Fi and turn off Wi-Fi calling off, toggle Bluetooth on for about 10 seconds or so, toggle Bluetooth off, toggle Wi-Fi and Wi-Fi calling back on. 8/10 times this works for me, the other two I have to restart the phone.

I have the T-Mobile ASUS router so that's not the problem, and I've had several routers over the years through Comcast, CenturyLink, third Netgear, etc.. they all do it. It doesn't matter if I'm on my Wi-Fi network or not, the phone's going to produce an error with Wi-Fi and that's just all there is to it.

It's still a convenient app if you're in an area that has zero service but I am surprised that 8 years later this problem still exists without T-Mobile support being very knowledgeable about the situation. I've received a lot of answers from them but nothing has ever made the issue go away.

Check the channel your wifi router uses---I think it has to be 2,6 or 11. Don't quote me on that though. I use 6 and it works fine. I haven't been terribly impressed by the wifi calling on my phone. Resetting the router can help, assuming you've had success at some point getting through. It could be relating to other settings on your router--check security/firewall issues.

You may need to call Comcast to make sure you or they can configure UDP port 4500 on the router for T-Mobile configurations.  T-Mobile also offers an ASUS TM-1900AC Cellspot for either free or a $25 deposit.  Saves the router rental from Comcast and ensures proper setup by default.

You will need to ensure that certain ports and protocols are not locked down on your firewall. IP Range & Port to be whitelisted:

208.54.0.0/16 Port UDP 500, UDP 4500

66.94.2.0/24 Port 443

66.94.6.0/24 Port 443

66.94.7.0/24 Port 443

66.94.8.0/24 Port 443

66.94.9.0/24 Port 443

66.94.10.0/24 Port 443

66.94.11.0/24 Port 443

Comcast might be able to assist, given it is their router.

Thanks everyone for all of your invaluable advice!  I went out of town with the phone and, when I logged onto my other wi-fi network at a different location (using my own router and NOT the one I rent from Comcast), the phone worked beautifully on the wi-fi calling.  I'm now convinced that it has something to do with the router at my other location in Maryland and I will check it out when I get back there in a week or so.

Make sure your E911 address is selected in My T-Mobile - Profile - Account Settings.

Thanks for your quick reply.  I just checked my settings and the address is correct.  Any other ideas?

Are you using your own router or Tmobile personal cellspot router?

I have a router provided by Comcast. 

If the original poster has an Arris gateway, WiFi Calling will not work, period. I believe it has something to do with the gateway sending an IPv6 address to the phone.

With straight IPv4 addresses coming from a separate router, WIFI Calling works perfectly.

Port settings have no affect, since I once tested this by complately disabling both IPv4 and IPv6 firewalls on the gateway and WiFi Calling still didn't work afterwards.

Have COMCAST Xfinity and LG Q7+ phone in an area with little-to-no TMobile cell service so I rely heavily on WiFi calling.  Unfortunately, WiFi regularly drops and fails to reconnect or connects with Reg99 error.  This is a real pain when trying to do two factor authentication with bank accounts and I can't receive an SMS text!  Often the disable/enable wifi calling suggestion works, but sometimes not.  Also, wife and I have identical phones.  It works on one phone but not on other, but not always the same.  Sometimes mine works and hers doesn't; sometime vice versa.

Very frustrating!