What does 'Failed to synthesize voice' mean?

There are a few reasons why this error would occur.

• If your current plan has expired, then all premium features will be disabled.
• If you are on a Basic plan but are using a Pro voice.
• If your payment method has failed, due to which your plan has not been renewed.
• If an invalid IPA has been added to a particular word.
• If an unrecognized character is present in your script. (Recommend: Paste text as plain text using Ctrl/Cmd + Shift + V)