No Bill Credits!
Save $200 instantly when you buy a Verizon Galaxy S9, S9+
Receive a $200 instant credit when you finance through the Verizon device payment plan. Activation required.
$200 promotional credit applied instantly; remaining balance of device to be paid after 24 months. 0% APR.
This offer is for existing Verizon customers or you can become a Verizon customer
Won't let me upgrade just add a line shows when I attempt to buy
Probably your phone was not paid off yet. I had the same issue, so I paid off my current phone, and only after that I could proceed to upgrade my current line.
Extra 7.5% off with one of the following discounts
Samsung Education discount [samsung.com]
$480.99 or $20.04 a month for 24 months for the Verizon S9
$591.99 or $24.67 a month for 24 months for the Verizon S9+
I would NOT recommend the trade-in program.
Maybe a worthless phone you just want Samsung to recycle for you and give you an extra $25 discount
Trade-in FAQ [samsung.com]