This problem is still occurring in March 2017! Confusingly I get the message "Successfully created test account" but then when I drill down into the account details it says "We experienced some issues on our end while creating this Sandbox account. Please delete it and try again." Deleting and recreating accounts doesn't fix the issue. I've tried entering different field values like somebody else in the forums suggested, but that never worked either. I cannot create Sandbox business account nor Sandbox apps for the REST API. This blocks me from using Basic client integration because I can't create a client ID.
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