My hotspot is giving a failed message "we can't set up mobile hotspot. Turn on Wi-Fi" but my Wi-Fi is on?

[clemynhu]

In trying to switch on my mobile hotspot, it gives me a fail message saying "we can't set up mobile hotspot. Turn on Wi-Fi" but my wifi will be on?

 

[GreyCatz]

Which device prompts the error message - the smartphone or the laptop?