I'm not sure what the lump sum was for.
If it was a disbursement from a retirement plan, did you get it after January 1st. This would not be taxable until 2020. If it was from your retirement plan and received in December, you will get a FORM 1099-R that should be posted to your 2019 tax return.
If it was for something like a severance payment you should get a W-2 to reflect that.
In either case I would suggest that you contact your employer and see if they have issued the documents.
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