iPhone 3GS w/ Tracfone

Hey all. I recently bought a prepaid Tracfone plan with 1200 minutes, 1200 texts, and 3GB of data to use with an iPhone 3GS. The phone is in good working order, the calls and texts go through perfectly, but whenever I try and use the data, I get this message:

Does anyone know a way to fix this? Is my iPhone incompatible with the plan I bought?

Link to plan: https://www.ebay.com/itm/283493024108?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Dccdc167c79404931979ceb4adc802aca%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D283493024108%26itm%3D283493024108%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DTracFone&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A9500a7f5-0112-11ec-ac37-a2ffbcf65d0c%7Cparentrq%3A5f73229817b0a9f736b3977cffff2eea%7Ciid%3A1

The iPhone is running iOS 6.1.6 and is unlocked. Any help would be appreciated. Thank you!