When turned off, your in-game Steam Overlay causes your micro-transaction purchases to fail. To turn on the Steam Overlay:

1. Go to Steam on the top hotbar.

2. Select Settings.

3. Select the In-Game tab, and then turn on Enable Steam Overlay while in-game.

To learn more about Steam Overlay, check out Steam Support.

Purchases within the in-game store require you to confirm your selection before completion. This error message may appear if:

1. You cancel the purchase before it completes.

2. You experience any kind of service interruption during the purchase process.

There's a limit to the number of times that you can purchase some in-game store products. Some examples of these limits are weekly purchase limit, and single, one-time only purchases. If you try to make a purchase that falls outside these limits, you'll get the error message.