I don't know about disability, but when we tried to get Medicaid for my grandma (who had dementia and bipolar), the people in the office kept losing things or kept saying that we never sent them anything. We had physical copies, though, as proof, and we had to use the copies to tell them, "no, we already handed this to you, IN PERSON. Here's the proof, and we have the dates we dropped them off at."

Maybe I'm just negative, but I don't trust most government employees with critical matters like this. They conveniently "lose" things or misplace things.

Online could work if you get an email receipt, but be forewarned... (1.) there is no guarantee they will check online applications in a timely manner, and (2.) they could come up with some BS excuse like, "well, we never got anything online. Looks like it's your computer's fault," or they'll be lazy and say, "the paperwork needs to be processed by someone. We don't do it. We have someone else do it. Call 123-4567." Then when you call the number, you're stuck on hold for like 2 hours (literally) because everyone else is calling at the same time.