Got an email saying refund is on its way & will be deposited in 1 business day, but on the IRS where’s my refund page there’s an ALERT code 151. Could this be an error?

TurboTax only uses estimated dates based on the IRS's claim that the majority of refunds are issued within 21 days of acceptance...not all returns get processed that quickly.

The IRS website will have the most current information regarding your refund.

This message means your return is under review for an unknown reason. The IRS will be sending you a letter about this, generally asking for proof of income or deductions. Don't panic, and wait for the letter to arrive.

See the actual text here: IRS Tax Topic 151