Hi there
Please try this
Toggle Connections: Turn Airplane mode on for 10 seconds, then turn it off. If you are on cellular data, switch to a stable Wi-Fi network.
Disable VPN: Temporarily turn off any active VPN configurations under Settings > General > VPN & Device Management, as they can block Apple validation servers.
Restart Your iPhone: Perform a standard restart or a force restart (press and quickly release Volume Up, press and quickly release Volume Down, then hold the Side button until the Apple logo appears) to clear temporary background glitches.
Check for Background Indexing: If your phone was recently updated, let it sit connected to power and Wi-Fi for a short period to finish background system indexing.