In every case in the Gospels - every case - where Jesus forgave sin (
Luke 5:20, 7:48 and others), He told the sinner that their sins were forgiven. They had undeniable assurance of their forgiveness, just like Catholics and Orthodox do. Ask your Baptist friend what he hears in his ears, when his sins are forgiven. And if he hears nothing, isn’t he dangerously presuming that they are forgiven, since that is not how Christ taught it?
OK, Saint Paul should strike a chord with him.
2 Corinthians 2:10 “What I have forgiven, if I have forgiven anything, for your sakes, has been in the
person of Christ.” KJV, D-R, Knox and other good translations.
“In persona Christi” - is exactly how Orthodox and Catholic Priests have forgiven sins for 2,000 years now. Ask him what the Baptist convention was doing 2,000 years ago.
2 Corinthians 5 “Be reconciled to God” “Given us this ministry of reconciliation”
James 5:16? “Therefore, confess your sins to one another” - I’ll bet he doesn’t even do that! Altar calls do not count, as they are not bibical.
However, Baptists are indoctrinated in anti-Catholicism. You are probably wasting your time, as only the Holy Spirit will convict him of error. Do you pray before the Blessed Sacrament? Go there, and pray for him - that will do more than 1,000 conversations.