Box 13 on Form 1099-R is for the two letter state abbreviation and the state tax ID number. If you don't have any state tax withheld in box 12, you can just leave the field blank.
If you do have a number in box 12, you can enter the Payer's TIN or EIN in the second part of box 13. This is usually located just above or below the payer address.
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