Hi @ethanic17 and welcome to the forums.
May I ask you, why do you want to switch from Paper to Spigot Server?
Paper is a high-performance fork of the Spigot Minecraft Server that aims to fix gameplay and mechanics inconsistencies as well as to improve performance. Paper contains numerous features, bug fixes, exploit preventions, and major performance improvements not found in Spigot.
Regarding your question could you please try to download the jar file in the ~/server directory? I believe this is the right place to put it, but I haven’t tried this before, so please let me know if this works for you.
Georgia