pushchairs and online checkin
Ryanair only allow infants 0-2 to carry one piece of baby equipment i.e. pushchair. I presume that as you are checking in online, then you must be travelling with a child, 2+, therefore technically you might have to pay for it as baby equipment. However, it all depends on the ground staff and whether they pick up on this. If you are checking in online and taking a buggy, then you must go to check-in anyway to get the buggy tagged, as it will be going into the hold. If you want to be really cheeky just turn up at the aircraft with the buggy and online check-in, however this can cause major issues for the ground staff, and if it could cause a delay, the buggy could get left behind.
Best to check-in online and go to chek-in, try your chances with the ground staff! Hope that helps.