You don't know ?Where in the bible was anyone saved by saying a silly prayer like the so-called "sinner's prayer"? Post the scriptures! That silliness is the essence of their false message.
When a sinner comes to be led to Christ and repent of their sins,they typically do so by praying.As a sinner.
Technically, any such prayer is able to be described as a sinners prayer due to that fact
If you haven't prayed and asked forgiveness of your sins,that they be put under the blood of Christ so that God remembers them no more and you are then redeemed of that former sin debt, I urge you to listen in your heart for Christ knocking at that door.
Have you seen the picture of Jesus knocking at a door? It's a classic.
What is often left unnoticed in that image?
There is no doorknob on the door side that's facing Jesus.
No one comes to Him unless the Father calls them.

That's not false doctrine. That's the Gospel Good News.