We had a similar situation with my son’s DSA application form a couple of months ago. Similar situation - we had to use the paper form as only applying for DSA, not finance.
In our case, first choice uni said to just send it in, with that section completed (so uni and course details) but missing the university signature and stamp, with a note explaining we lived too far away to get it completed by hand. And Student Finance would reach out directly to the university to confirm.
So we did that, and then 3 weeks later, got a strange letter back from Student Finance saying they couldn’t find our course details, and a vague instruction to react out to the university to “get in touch and confirm”. We tried again to reach out to the university, but when they responded they didn’t know what to make of, and just gave us the original advice again.
At this point, we were beginning to panic, as more weeks went past. However I got on the phone jointly with DS (must be with DS) and we phoned Student Finance, and it was all sorted out that afternoon.
So in short, the paper process isn’t perfect (probably due to small volumes of people going that route), but send it in as complete as you can, and then if you need to speak with Student Finance directly to sort it out after a few weeks then they are really helpful.