First of all, head to Settings > Wi-Fi, forget this network and then join again. When joined, tap info of your network and make sure that Auto-Login is on.
How to fix an iPhone that's not connecting to Wi-Fi Restart your iPhone. ... Remove your iPhone case. ... Check to see if your Wi-Fi is turned on. ... Check your router. ... Check your network settings. ... Reset your iP
Resetting network settings on your iPhone can solve many connection issues, but it will erase all your data related to networks, like your saved WiFi passwords.