DO you have a good fully charged battery?
Is it isolated via a battery disconnect switch?
Fridge requires DC power to function
And WHAT fridge do you have.........numerous models by by MFGs.
Not trying to be rude it's just your question is like asking "I have a piece of rope------how long does it need to be?"
Brand/Model of appliance is better info than which RV you have.
Details of what it does and doesn't do is even better info.
It sparks but doesn't light, it doesn't spark, it lights but doesn't stay lit, it doesn't/it does. OK