We are told in John 14:16 Jesus says, “Whatever you ask in my name that will I do that the father may be glorified in the son.” So, from that we realize that there’s an explicit passage about praying in Jesus’ name. But more importantly, the truth it points to is the larger truth found in the New Testament that we have access to God the father through Jesus. When Jesus was crucified, the veil of the temple was split in two from top to bottom. And Hebrews tells us that we then have access to God through the veil that is his flesh. So that veil, that several inches thick of material that separated the Holy of Holies, where the presence of God was manifest there over the arc of the covenant, only the high priest could go in. Only he once a year after a week’s preparation, that now through the death of Jesus, anybody has access to God, but they must come through the veil of the flesh of Jesus, through the death of Jesus Christ.
https://bible.knowing-jesus.com/topics/Asking-In-Jesus-Name
So, our access to God is in coming through Christ and His righteousness. Hebrews says that we come in his blood. So, it is through the death of Jesus Who we have access to God, and praying in Jesus name is a theological shorthand for expressing that. That we have no righteousness of our own, that God will receive us as it were covered in the blood of Christ. God will receive us having been United with Christ.
When we say, “In Jesus’ name” it is as if Jesus Himself said it. When we pray in Jesus’ name, we pray in the Spirit and our wishes and God’s wishes are the same so that we only pray and ask for what it is that God desires to give us, which of course is the very best for us.
Amen is commonly used after a prayer, creed, or other formal statement. It is spoken to express solemn ratification or agreement. It is used adverbially to mean “certainly,” “it is so,” or “so it be.” Amen can be used in formal prayers within a prescribed script.