Every time you try to purchase in the Steam Store, you may receive an error message indicating that an unexpected error has occurred. This error message may prevent the user from purchasing important items in the Steam Store, and you may not be able to complete the purchase.
A detailed error message may look like this: An unexpected error has occurred. Your purchase cannot be completed. Please contact Steam Support.
Other Steam errors can prevent the user from launching games on Steam, but this error will prevent the user from purchasing from the service store completely. Here’s how to fix the Steam store error “Unexpected error occurred during purchase”.