@Solla-topee 

Thank you for your answer

-The router is FASTGate GPON model FGA2130FWB connected to the network with an optical fiber

-Client is a laptop with WINDOWS 10 OS (italian lnguage)

-The Primary WIFI network name (redefined) is ROCCATI-GAR9. (This network can be connected without problems)

-The Secondary extended network name is ROCCATI-GAR9_EXT protected and the automatic connection flag is on .

Selecting the ROCCATI-GAR9_EXT WIFI net and pressing the 'CONNECT' button  here the following steps

1)           SYSTEM 'Immetti la chiave di sicurezza' ( insert the security key)

2)  I enter the security key ( the same of the modem/router  primary network) and push the 'AVANTI' (go on) button

 note  --If i try to enter a wrong security key, the system notify en error message. So seems that the the security key is accepted

3)           SYSTEM ' Vuoi consentire al PC di essere individuabile per altri PC e dispositivi di rete? (YES/NO)

4) I YES

5) SYSTEM 'Non è possibile connettersi a questa rete'

Up to now I have not tried the WEB initialization procedure ( not so clear to me)

Thank you again

@albi42 

Thank you again

The problem is solved. It was necessary to redefine the secondary network name deleting the _EXT suffix so to make the primary and secondary name the same.

This was not possible with the WPS procedure (as far as I know). I have used the Tplink Teather app.

However it is not clear to me wy the extended net default name was not accepted.

Best Regards

Alberto Ancarani