Kind of reading between the lines, it looks like the NFL pays for "Pro Day's". It's kind of whacky in the times of COVID. Normally you'd have the "NFL Scouting Combine", which has been canceled again this year, however the combine is invitation only and held in Indianapolis and is paid for by the NFL. Pro Day's are more of an open try-out and please note that Pro Day's are normally held in addition to the Combine and not in lieu of it.
"Each university has a Pro Day, during which the NCAA allows NFL scouts to visit the school and watch players participate in NFL Combine-like events and drills. Some smaller universities join with nearby schools. They are essentially job fairs for prospective NFL players."
For information on the Scouting Combine