Fixing App Store “Could Not Complete Purchase : Unknown Error” Messages

Aug 13, 2014 - Leave a Comment

App Store We could not complete your purchase - Unknown Error

Typically you can download anything from the Mac App Store without incident, that’s the way things are supposed to work. Sometimes things aren’t so hunky-dory, and one of the more peculiar errors from the App Store is the incredibly vague “We could not complete your purchase – Unknown Error” message.


Having experienced this error message myself not long ago when updating apps on a Mac, and some time in the past when updating OS X, we received a question on Twitter (yes, you can follow us there and ask us questions!) about the exact message as well. While it’s frustrating, the good news is that it’s usually very easy to fix with either one or both of the following steps; verifying the Apple ID, and – here’s where it really gets fun – accepting everyones favorite iTunes Terms And Conditions.

Verifying the Apple ID in Use is the Same in iTunes & App Store

  1. Verify in both the Mac App Store and iTunes apps that the same Apple ID account is used for both apps – if it’s not, log out so that both apps have the same Apple ID account
  2. Quit out of the Mac App Store and quit out of iTunes (yes, quit out of iTunes if it’s open)
  3. Relaunch the Mac App Store and try updating or downloading the app again, it should work flawlessly

Simple solution, right? The problem appears to be triggered by an issue with the Apple ID accounts associated with the App Store, making it frequently experienced by users who have different Apple ID’s for whatever reason. This is yet another reason to try and keep a single Apple ID in use for all of your user activity, though there are certainly times where that’s not possible, particularly for international users.

Check & Accept iTunes Terms & Conditions

Still seeing the “Unknown Error” error message and it’s preventing you from downloading anything? You may have an issue with the iTunes Terms & Conditions. Yes, seriously. All 50+ pages of those exciting terms and conditions may be the cause of your inability to download and update apps. The good news is this is also super simple to fix:

  1. Launch iTunes, or quit it if it’s already opened but has just been updated and then relaunch iTunes
  2. Accept the new Terms & Conditions, after reading them thoroughly of course!
  3. Quit and relaunch App Store

You should now be able to download from the App Store as intended.

This solution was found by one of our commenters (thanks Mike!) , who discovered some time ago that if you update iTunes without choosing to accept the Terms and Conditions that have changed, this error persists in both iTunes and the Mac App Store until those new Terms & Conditions are accepted. Curious, indeed.

iTunes Terms And Conditions

A similar issue is sometimes identified as Error 100 in the App Store or an inability to connect to the appropriate store, which is also resolved by simply logging out and back in to the App Store in question, whether iTunes or the Mac App Store.

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Posted by: Paul Horowitz in Mac OS X, Troubleshooting

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