If you are entering an employer's state ID number in Box 15 of Form W-2 and you see an error message, this may mean that the format of the number does not conform to that state's requirements. Each state may have its own rules about the format of the ID number. Some have a specific number of digits and specific characters peculiar to that state. See if the number in box b of the W-2 is different and will work.
If the TurboTax error message asks you for a state ID number in a specific format, such as needing exactly 9-digits and ending in XYZ, then enter any value that conforms to that format. Otherwise, you could try entering a series of 9s.
If you can't get information from the payer, you can also look on your state's Department of Revenue website for information about the employer ID number format required.