I met the same problem for my family who is self-employed, over 65 and not receiving CPP, have tried many times but the schedule 8 doesn't show up.
The support of Ufile says it only works on people who is receiving CPP and have a T4A slip. We don't have such a slip maybe that's the reason.
I called CRA this morning and the agent told me to file the NETFILE online, then attach a schedule 8 in paper and mail to CRA, this could work for the case. I think we will write down the information include name, birthday, SIN, and the reason in a letter explaining why the election is not applied through the software, so to see if they will do the adjustment from their side.