"Code BB—Designated Roth contributions under a section 403(b) plan. Use this code to report designated Roth contributions under a section 403(b) plan. Do not use this code to report elective deferrals under code E." See the W-2 Instructions.
Code BB means that your employer believes that this amount represents contributions to a Roth 403(b) plan. If you think that that is not correct, then you need to file an extension, pay whatever tax is due at IRS Payments, and talk to your employer tomorrow.
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