MetaTrader is currently experiencing technical issues with the download of its platform on IOS devices.
We advise our clients to keep the MetaTrader4 and MetaTrader5 apps downloaded on their devices. Downloaded apps should not be having any issues and may be used normally.
Alternatively, please view the below solutions.
If you have never downloaded MetaTrader and would like to - Kindly wait until the issue is resolved from MetaTrader's side.
If MetaTrader is not currently installed on your device but was previously - Follow the below steps.

Tap on your Apple ID icon.
Tap on the Purchased option for more information regarding your apps.
Search for MetaTrader4/MetaTrader5 and re-install by tapping on the cloud icons.