Everything is on the latest firmware and after reset the default account password works ok. I can enter the web interface of omada and the oc200 local interface without any issues, so I know the password for them. I haven't used the controler to change the password on any device.

This is one of my problems, the controler assings a new password to the EAP and router and fails to adopt them. Then I try to manualy adopt tham and I get a invalid login/password.

@NikosK I know this will sound annoying and unhelpful, but are you sure you followed that guide to the letter?  Starting with a fresh oc200 and ER7026? I had the exact same problem as you with having incorrect passwords and then followed the guide and everything worked on my first try.

@NikosK 

i didn't think of this yesterday but there is also this artical that may help.

https://community.tp-link.com/en/business/forum/topic/245838

Thanks for all the help provided. I removed all the omada devices and I will reset them again and create an ofline network in order to see if I can adopr all the devices normaly. I will post my results.

@NikosK In the end, were you able to adopt ER7206 ?

I have a similar configuration, OC200 & ER7206 both installed on a remote location. IP class ..1.x

They were working without issues but once I've tried to adopt ER7206 I've lost the internet connection (I tried to do the config using a remote connection).

Imagine my frustration ... :)

Working with someone on the remote location I was able to access OC200 and forget ER7206 then change the IP of the remote PC to class ..0.x and access the new IP of ER7206 ..0.1

It seems OC200 changed the IP of my router from ..1.1 to ..0.1 

My problem now is that no comnination of user/password is working, not oc200 user/pass, not the ER7206 user/pass not admin/admin .... nothing and on top of that I get the message that the maximum number of login attempts has been exceeded and I can try again in 2 hours ... :o(

I thought this type of enterprise equipment should work without any issues. OC200 found and displayed the correct IP of ER7206 on class..1.x, OC200 was also on the same class. I never imagined that OC200 will change the IP of the router to ..0.x class on adoption. Why would you do that ?