Aireplay deauth not working

i´m new to this but trying to learn.

i am using Kali and playing around with some WiFi hacking. i am trying to catch WPA2 handshakes and find hidden SSIDs, i know the basics of it but have one problem.

lets say i do find a hidden SSID i want to take a look on, i se the network, find the BSSID of it, lets say it is on channel 6, i focus airodump on channel 6 and go in to aireplay and send a deauth to that BSSID. all clients on that channel get kicked off, but, the problem i do have is that the clients are connecting to another channel, lets say on the 5G spectrum. and because airodump is not looking at that channel i do not get the handshake.
and i can´t set airodump to scann all the channels becouse then aireplay just get errors for wrong channel.

anyone have any tips or tricks for this?

(using my own network that is two ubiquiti APs and just my own phones and such as clients.)