@leandersc What are the model numbers of the 2 routers? Are they both TL-WR841N? What is the current network topology/diagram? How do you connect them together? And what are their operation mode...

@Spentit Is it 5GHz-1 or 5GHz-2 cannot be connected due to the incorrect password ( even though it is correct)? If all the devices have the same issue--failed to connect to it? Have you tried to...

@Tale Not sure whether there is any special settings need to be done on the AirPort Extreme 5th gen cause the AirPort Express works fine. You can contact Apple tech support to get some help first. Or...

@sdhk What is the model number of the AC750 you ask for? What is the current network topology/diagram? What is the firewall means? Is it a regular wireless router? Do you want to use the firewall to...

@Cristian2 Thanks for your reply. You can take your time to test its performance, any further problem, just let us know.

@Smitty124 Thanks for your reply, glad to hear that you got it fixed by adding an outdoor AP. Now you can enjoy the internet. If need any further help, do not hesitate to contact us.