Based on what?
Then demonstrate to us that it does exist.
You are out to prove there is no existence above and beyond the physical. For you it's just never going to be there.
The "based on what" and the "demonstrate to us" I mentioned earlier requires going to the Source, the Creator of all that we see and know. God is Spirit. God is above the natural. God is eternal, not of elements. His knowledge of you this moment and every moment is not shallow but as high as the farthest galaxies. He knows every detail about you. Every moment. HE IS THE ONE TO TURN TO, NOT WORDS OF MEN.
People need to go to the Source for evidence and the demonstration of the Spiritual Realm and what embedded things through His intelligence He has to reveal in the physical realm that reflects aspects of the Spiritual.
I Corinthians 2:4,5 the Apostle Paul stated similar - "not in persuasive words of wisdom [the existence and witness of God] but in demonstration of the Spirit and of power".
It requires the involvement of the Source. It requires the Spirit of God demonstrating His Power - the words of men is not what one needs and should seek.
As God through His Spirit was with Paul to demonstrate what to believe, and where to place one's faith in the current unseen realm, the same exists today. We get glimpses, true spiritual revelations from God, true manifestations of Spiritual Powers from the Spirit of God.
This is what going to the Source will produce. This is what ones inquiring about higher life in our midst should obtain, and not stop short of or settle for anything else. Period.
That is why I have the confidence that I have in kowing of the Spiritual Realm. It is available for all who really seek to know IF such exist. We all do not know at the beginning. It is an obvious uncertainty. It begins as an IF, and big IF. But He is. Many have a relationship with Him that He brings about through Power from above the physical. And many have such faith through His Power.
To then tell these Spirit taught individuals that God does not exist reveals clear unawareness of the higher life in our midst. How people can come up empty handed about the Spiritual Realm through Naturalism.