The verse in Peter refers to spiritual healing. Not physical healing. God's gifts are freely given. God doesn't cruelly hold them back until we know the magic words.

Jesus was talking to his disciples in Mark 11. They would be given whatever they needed to fulfill their ministry. Not to satisfy their selfish desires.

Timothy and Paul both had health problems. Timothy was often sick. Paul had bad eyesight.

(1 Timothy 5:23 NIV) Stop drinking only water, and use a little wine because of your stomach and your frequent illnesses.

(Galatians 6:11 NIV) See what large letters I use as I write to you with my own hand!