Contradiction with Exodus 4:1
Exodus 4:5 states a demonstration of God's power through signs to make people believe, contradicting Moses' earlier doubt in 4:1 that they would not believe him even with signs.
Exodus 4:1: And Moses answered and said, But, behold, they will not believe me, nor hearken unto my voice: for they will say, The LORD hath not appeared unto thee.
Contradiction with Exodus 3:12
In Exodus 3:12, God promises His presence will be a sign, contradicting Exodus 4:5 where physical miracles serve as signs for belief.
Exodus 3:12: And he said, Certainly I will be with thee; and this [shall be] a token unto thee, that I have sent thee: When thou hast brought forth the people out of Egypt, ye shall serve God upon this mountain.
Contradiction with Exodus 7:13
Exodus 4:5 implies signs will convince, but Exodus 7:13 shows Pharaoh's heart was hardened despite signs.
Exodus 7:13: And he hardened Pharaoh's heart, that he hearkened not unto them; as the LORD had said.