Dear @EidVictor,

EAP shows "pending" in Controller, click in Adopt, but after some time, appears a pop-up error "Device adoption failed because the device does not respond to adopt commands", and EAP icon shows "Adopt failed" in red after some seconds.

The error means that the communication between EAP and Omada Controller is blocked. You may check the points below.

1. Ping the EAP on the PC that the Omada Software Controller is installed, ensure the EAP is accessible.
2. If you have VLAN settings in your network, ensure the EAP and Omada Controller are in the same VLAN.
3. Omada Controller communicates with the EAP via TCP/UDP port 29810-29813. Some anti-virus programs or firewalls may block this kind of packet.

    You may disable the anti-virus or firewalls (on the PC that the Omada Controller is installed) in your network first for checking.

P.S.: I have another EAPs working perfectly in the same Controller.

Is the working EAP connected to the same LAN or VLAN network? 

If you swap the two EAPs in the network, would the issue exist on the same EAP?

Dear @EidVictor,

My controller is running onto VPS instance, Debian 9, and I trying to use L3 adoption.

I'm already checked all incoming firewall rules of my server, and is correct (tested disabling all IPTABLES rules too, without success).

I think that actual ISP of local AP instalation thats blocking these inicial adoption packets. But don't have further information.

How can I verify this possibility?

Are the EAP and Controller in different networks?

What's the IP address of the EAP that you are trying to adopt? How about the Controller IP?

It would be helpful if you could provide a network diagram showing how the devices are connected with IP info.

If you are trying to adopt the EAP across the Internet, see the example in the FAQ below, you may open Port 29810-29813 on the Router.

How to manage EAPs at different places across internet using Omada Controller: https://www.tp-link.com/support/faq/2763/