Authorize.net Fraud Detection Settings
Authorize.net recently changed its default fraud detection settings. Due to that, you might be seeing "Held for review" errors when attempting to process a payment.
To avoid this from happening, log-in to your Authorize.net account and visit your fraud settings center by going to "Account > Settings > Security Settings > Basic Fraud Settings", and disable all the settings.
You likely have a few transactions that are held for review if you've seen this error. You should approve those transactions (declining would mark that payment as fraud), and then void the transactions.
Please contact us if you have any more questions regarding this matter!