As of 11/10/18, ToneWoodAmp users have been experiencing trouble with MIDI guitar 2 on Apple devices after updating to iOS 12. 

If you already have MIDI Guitar downloaded to your device, you will be able to update to iOS 12 with full app functionality. 

Please do not delete the app before you update to iOS 12. You will not be able to reinstall until after Jam Origin relaunches the updated version of MIDI Guitar. 

This issue is affecting MIDI Guitar 2 and not SampleTank. 

The following information was provided by Jam Origin:

What is going on?

MIDI Guitar for IOS is temporary out of the store, because the fresh install is not compatible with IOS12.

Jamorigin is working hard to bring an update.

What If you want to buy a new ipad/iphone for use with your existing MIDI Guitar purchase?

´IOS 12 is not supported yet for fresh installs of MIDI Guitar. Please wait a few weeks.

What If you want to update an existing IOS device with MIDI Guitar on it  to IOS12?

This should be no problem, just do not delete the app!

Can I (re)install a previously purchased MIDI Guitar on devices that don't have IOS12 on it?

Yes, if you have purchased our app and have an IOS device with IOS below version 12, you can redownload 

the purchased app and use it.

Please look at

How long will it take for MIDI Guitar to be sold again and compatible with IOS12?

Jamorigin is working hard on it. The updated version is planned to be available in the middle of January.