Sounds like the usual blade mechanism failure. The blade , cheap plastic, has a small cog moulded on the underside . This is moved by the blade arm piece which operates when you move the open / close lever at the front of the toilet bowl.
The part is circa £6.00 and freely available. I carry two spares . They have rescued Woosies at previous meets!
Yet again a very poorly cheaply designed caravan product. Better materials would certainly help.
Also agree with the other posts. Do not force it or you will cause more expensive damage.
Which model of toilet have you?