Remote extension is registered, no DND, but is unavailable

[LxLiberty]

Hi there, first post so bear with me

We have a FreePBX server at our main site and about 20 extensions.

We have recently installed a new router at our new site and connected it through an IPSEC VPN tunnel.
The new remote site has a production and a VOIP VLAN. The phone in question is connected on the VOIP VLAN, obtains an IP address, registers to the FreePBX server over at the main site, can make outgoing calls BUT if anyone tries calling the extension, they get the message saying the extension is unavailable. (From IVR direct dial or directly from another extension gets the same result.)

I have tried creating and registering with another extension, created firewall rules to allow any traffic between both Watchguard routers (From Any to Any=allowed)
All new LAN subnets have been added to Asterisk SIP settings.
Linux server has been rebooted
I tried to do a call trace while bein logged into asterisk with -rvvvv, but couldn’t really get anything useful.

Any ideas what could be happening ?

[LxLiberty]

I enabled SIP debug and made another call trace, in which i noticed I had “SIP/2.0 488 Not Acceptable Here” messages.

After some research I ended up changing the RTP encryption setting to “optional” instead of “compulsory” on the Yealink phone and it now rings !

Please let me know if there is a better way to do this or a permanent way to fix this as I don’t really want to have to change this option on every new phone that ends up at the remote site.