@rafaelP 

Have you managed to solve this yet?  I use EAP650-Desktop APs here but do not have any of them configured to use the FXS port.  I am a Movistar customer and therefore I am interested in the solution.  Presently, I use a Yealink SIP phone and it works perfectly.

Your problem is probably due to using the Monopuesto mode of the Movistar router.  I am not familiar with MikroTik routers but TP-Link routers allow you to set up a secondary connection along with the main PPPoE connection.  Setting up the secondary connection with a static IP in the 192.168.1.0/24 subnet and then creating a static route to the Movistar SIP network(s) in the 10.x.x.x range via 192.168.1.1 used to work for me some years ago.  I no longer use the Monopuesto setup as I had problems with the secondary connection after switching from the Tp-Link home products to Synology.  Since then, I have upgraded everything to Omada but have not yet tested the Monopuesto configuration as the current double NAT setup is working perfectly.

On the subject of the EAP650-Desktop and the FXS port, the documention is very poor or non-existent.  A new firmware update was expected out in April to fix several isuues but we are still waiting!

  @rafaelP

I must have overlooked the fact that you stated in your initial post that you were using a standalone ONT.  Thank-you for clarifying everything.

Out of curiosity, I have several questions:

1. What make and model of ONT are you using?  I may aquire one for testing.

2. What 3 VLANs are on the trunk ports of the managed switch?  The same 3 from Movistar (6, 2, and 3) or different VLANs that you have created?  If they are the 3 Movistar VLANs, which one is the native VLAN (untagged) on the trunks?

  @rafaelP 

Thank-you for the info on the ONT.  Let's hope that Tp-Link can provide more information on the FXS port.

  @rafaelP 

I just did some quick testing here but with a different setup.  After looking into the quick availability of the Huawei HG8010H and seeing that it is not readily available, I decided to test the FXS port with my current setup.

I am using the HGU in its native Multipuesto configuration with the Omada gateway connected to the HGU’s LAN port 1.  It’s a double NAT situation but works quite well.  No games here but I do use a WireGuard VPN and can stream video perfectly.  The Omada speed test shows some 950+ Mbps in both directions with a 1 Gbps fiber connection.  The Movistar UHD video decoder is connected via an internal VLAN to the HGU.  I also have a remote wall phone (standard landline) connected to the HGU via the dwelling’s telephone wiring.

For the test, I configured a Movistar profile under Call Settings with the following parameters:
Profile Name: Movistar
Telephony Provider: Other Provider
Registrar Address: telefonica dot net (replace "dot" with ".")(forum rules do not allow you to write the domain correctly)
Registrar Port: 5060
SIP Proxy: telefonica dot net
SIP Proxy Port: 5060
Outbound Proxy: 10.31.255.134
Outbound Proxy Port: 5070
Register via Outbound Proxy: Enabled

Under VoIP Device, I selected one of my 3 EAP650-Desktop APs.

Under VoIP Phone Number. I configured the following:
Provider Profile: Movistar
Phone Number: phone number (without the 34 prefix)
Username: same as phone number
Password: same as phone number
Device MAC: EAP650-Desktop under test selected

I don’t have an analog telephone to connect to the FXS port but apparently it isn’t needed.  To my surprise, after configuring the VoIP Phone Number, Registered immediately appeared under Status.

What this tells me is that the FXS port of the AP works and is compatible with Movistar.  The FXS port does in fact use the management IP address of the AP.  In your case, it would appear to be a question of routing between VLANs.  I also noticed that in your original post the Register field did not have an entry.

Now knowing that the EAP650-Desktop works with Movistar, I hope the above info might help you in finding a solution.

  @rafaelP 

Perhaps I should have mentioned that earlier but the confIguration settings are in the Omada controller. Attached is a screenshot.

Earlier today, I attached an analog phone to the FXS port to see how well it works.  Initially, there was a lot of line noise. Then I had to configure a Digit Map to get the phone to dial properly.  After dialing, the called number more times than not would not ring (I used my cell phone for testing) and just seemed to hang.  Incoming calls would sometimes not ring either.  The HGU showed the phone as being registered properly as did the Omada controller.  For a lack of time (and patience), I abandoned the testing and disconnected the phone from the AP. The bottom line is that I will never use the FXS port after what I experienced today.