WiFi connection on one device not working

Just for the sake of clarity, iOS runs on iPhones. Your Mac runs macOS. Using the correct term will help avoid confusion and will aid you when searching for assistance.

As to your problem, without any details about your Mac or network, it's difficult to offer specific suggestions, but perhaps something here will help:

If your Mac isn't connecting to the internet over Wi-Fi - Apple Support

Regards.

The OS can impact connection to WiFi if you have set up MAC address filtering or strict binding on your wireless access point or router because the default is for the Mac to randomize its Mac address. Otherwise I can't think of anything other than the obvious one that the password is incorrect. What error message are you getting when you try to log in to wireless with your Mac Mini?

(You said Mac Mini and IOS - I assume you mean MacOS)