- Is this your corporate iPhone? Then please contact the system administrator of your corporate
- If it is your device, in that case, do you have any profile installed by your corporate/organization/enterprise/School Management?
- Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
- Please contact the system administrator of the organization who provided the profile to you

For a device-specific problem, resetting network settings (Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings) is a good first step. If the issue persists across multiple devices, it’s likely a router configuration issue, which can often be resolved by contacting the ISP or checking settings like MAC address filtering, DHCP settings, or Wi-Fi band compatibility.