If you received this lump-sum payment in 2017, it needs to be included on your 2017 return; if received in 2018, it needs to be included on your 2018 return.
I've attached two TurboTax FAQs: one regarding the lump-sum payment reporting procedure, and one relating to amending your return, in the event that you need to amend your 2017 return to report the lump-sum transactions.
What is a lump-sum Social Security payment?
