Idaho does not have a convenience of the employer rule. It appears that this bonus is not considered Idaho-sourced income as long as the taxpayer neither lived nor worked in Idaho in 2023.
https://tax.idaho.gov/taxes/income-tax/individual-income/idaho-source-income/
Therefore, the income does not appear to be taxable to Idaho.
If the employer gets a W-2 showing Idaho income and/or withholding, they will have to file an Idaho non-resident return and report zero Idaho income. (In Turbotax, you have to manually allocate your income to each state. You would allocate zero income to Idaho.) With zero income, you would be due a full refund of any withholding. However, the issuance of a W-2 with Idaho withholding may cause Idaho to question the circumstances and send a letter to the taxpayer asking for more information and proof, so keep copies of emails, contracts and so on, that demonstrate that you did not work or live in Idaho. (You can visit Idaho for interviews and house hunting and that by itself will not make the bonus taxable to Idaho. But you will want proof that your actual job didn't start until 2024.)
Alternatively, the bonus may be reported on a 1099-NEC or 1099-MISC. That could complicate matters, since a sign-on bonus is considered wages and should be on a W-2, and that would be easy to to if the job started in 2023, because the taxpayer would already be getting a W-2. If the employer issues a 1099 and not a W-2, we can discuss that further.
@michael-walawend Did you receive the entire gross amount of the bonus or a net amount after tax withholding? Do you know if there was withholding for federal income tax, state income tax, social security tax, and/or medicare tax?
