Starting this morning, I can't charge with sandbox

I'm also seeing this on a iOS 13 device. It prompts me twice for the password, then fails with Error Domain=SKErrorDomain Code=0 "Cannot connect to iTunes Store". I even tried creating a new sandbox test user and still run in to this same error.
iOS 14 devices can purchase no problem.

This looks like a bug report issue - IT would help to capture a console log with the StoreKit profile installed. Here's the instructions to install the StoreKit profile, capture the console log, and to submit a bug report.

BEGIN
Here are the instructions to install the StoreKit profile
Install StoreKit profile to an iOS 11+ device
Please login to the Apple Developer Bug Report - Profiles and Logs website
<https://developer.apple.com/bug-reporting/profiles-and-logs/> using Safari on the device you will use to replicate the problem with.
Click the “Profile” URL associated with the “App Store/iTunes Store for iOS” item. You will download the “itmsdebugging.mobileconfig” file.
For iOS 12.2 or later, you will open the Settings app -> General -> Profiles & Device Management -> iTunes and App Stores Diagnostic logging -> press Install
For devices with less than iOS 12.2, - PLEASE RESTART THE DEVICE

Review the following article on testing StoreKit apps
<https://developer.apple.com/documentation/storekit/in-app_purchase/testing_in-app_purchase_transactions>

CAPTURE THE DEVICE CONSOLE LOG - connect the device to a macOS X Sierra system (macOS X 10.12.x or newer)

1. Launch the Console app on the macOS system, and select the device in the left side of the Console window

2. Before starting the iOS app, click “Clear”.

3. Start the application and perform the steps to replicate the problem.

4. When the issue occurs, save the contents of the Console log

Check the contents of the console log for the string “fetchSoftwareAddOns”. If this string is not present in the log, the profile was not active. Please re-install the StoreKit profile and make sure to restart the device.

If the string is found, this indicates that the profile was successfully installed and is active. Save the entire contents of the console log - starting from the point that the app is launched to when the problem occurs - to a text file.

To submit a bug report, please use the Apple Developer Feedback web page -

<https://feedbackassistant.apple.com/>.

Enter the “Feedback Assistant” page and login
Click on the Compose icon to start a new bug report

Start by clicking on the appropriate OS button - “iOS and iPadOS”, “tvOS”, or “macOS”

• In the “Descriptive Title” field, enter an appropriate description.

• In the “Problem Area” field select “StoreKit”

• In the “Type of Feedback” select “Incorrect / Unexpected Behavior”

• In the “Describe the Issue” section enter the following

  • application ID (and In-App Purchase identifiers if appropriate)

  • sandbox environment

  • the name of the test user account and the localized App Store used to make the purchase from.

  • the instructions for finding the “Buy” button to purchase the In-App Purchase item.

(if the app is not in English, please provide screenshots)

• the problem description in detail.

5. If you have captured a console log - drop it onto the “Drop Files to upload”.

rich kubota - rkubota@apple.com
developer technical support CoreOS/Hardware/MFI

We've been encountering this exact same issue since October 16th. iOS 14 devices with sandbox test accounts can perform IAP fine after being asked for a password twice, but devices below iOS 14 are reporting the error code 0 'Cannot Connect to ITunes'. Our app was build with XCode 11.3.

Has anyone been able to find a solution to this? It's really hindering testing.

With our team spread out and working from home, we are unable to follow the instructions to get the logs required to submit a bug report.

Sent a bug report.
Found an interesting (for server specialists) line in my log:
"IDSService send request failed. Error: Error Domain=com.apple.identityservices.error Code=7 "Could not find valid account" UserInfo={NSLocalizedDescription=Could not find valid account}»

This seems to explain the reason why we can no longer buy/test our IAPs.

Any solutions so far? It's really frustrating since it makes testing impossible.

Engineering is investigating sandbox buying issues with iOS 13 or earlier. rdar://70363298

me too.
I'm using Unity IAP.

this problem is fixed around 3hours ago.

App Store Sandbox - Resolved Issue
https://developer.apple.com/system-status/