@Red_Falcon 

Thanks for reaching out. I understand that you are experiencing issues using a VOIP adapter (such as the Grandstream HT802) with your Deco Mesh system, where VOIP calls are not working properly, even though the same setup works with other routers.

Please note that some Deco Mesh systems (for example, the Deco 73-DSL) support telephony features (VOIP) and allow you to connect a VOIP phone directly using an RJ11 phone line. However, most Deco models, including the Deco BE65, do not have built-in VOIP/telephony ports and instead rely on your network to pass VOIP traffic to your VOIP adapter.

To troubleshoot VOIP issues with Deco Mesh:
1. Check if your Deco model supports VOIP natively. Most Deco models do not, so you will need to use your VOIP adapter as you have been.
2. Ensure SIP ALG is disabled. SIP ALG can interfere with VOIP traffic. You have already done this, which is correct.
3. Set up port forwarding for SIP and RTP ports. Make sure you have forwarded the correct ports for your VOIP service and that the IP address reservation for your VOIP adapter is set up correctly.
4. Check for double NAT issues. If your Deco is behind another router or modem/router combo, double NAT can cause VOIP problems. Consider switching your ISP device to bridge mode or setting your Deco to Access Point mode.

For more details and step-by-step instructions, please refer to this FAQ: https://www.tp-link.com/en/support/faq/3340/

If the above steps do not resolve the issue, please contact TP-Link support with the details of your configuration and troubleshooting steps for further assistance.

  @Red_Falcon 

Hi, welcome to the community.

The suggestions shared by HelpFilxDecoApp are very helpful.

Is Deco BE65 the only router you have connected to the internet? You can check whether the IPV4 address on the Deco App is the same as the IP address displayed here https://whatismyipaddress.com/

Wait for your reply.

Best regards.