Smart RGB bulbs do not want to pair

I’m trying to pair 2 smart bulbs (B05-BL-A60). The app DOES find the bulbs but when I then click the blue ‘+’ sign the bulbs themself cannot connect to my network: Incorrect password (?).
This is also the case when trying to connect in Compatible mode.

My home Wifi is delivered through wired AccessPoints (1 on each floor). They all have the same SSID/pwd. It looks like the bulbs don’t want to connect through these AP’s, because when I switch this wifi off and turn on the wifi from my ISP-modem/router (same SSID/pwd): everything works fine and I can connect the bulbs and create scenes, the works!
But as soon as I disable this wifi and turn on my AP’s the bulbs show as Offline and do not respond to the scenes I just created.

The reason I have to use the AP’s is because the modem-wifi just doesn’t make it to the 2nd floor.
I also tried a ‘new’ wifi-network with another SSID and pwd, but when I try to connect the bulbs the same old message appears: wrong password.

Does anyone have a clue how I should proceed?

Kind regards,