Once flying on UA, the UA web site would not allow me to OLCI. What an annoyance, given the typical huge (1 hour long) check-in lines that I had come to expect on UA. Turned out that there was someone else with the same name on the same flight, and that disallowed OLCI.
At the time, UA was giving bonus FF miles for OLCI. I was able to get the bonus miles after calling them and saying that I attempted to OLCI but was disallowed by UA for reasons other than normal OLCI limitations at the time.
No idea what Spirit will do or why they are refusing OLCI for you (and whether it is something specific to you or a general issue).