Contradiction with Genesis 15:18
Joshua 13:20 lists territories within Moab allocated to the Israelites, whereas Genesis 15:18 describes God's promise to give Abraham's descendants land from the river of Egypt to the Euphrates, not limited to Moab.
Genesis 15:18: In the same day the LORD made a covenant with Abram, saying, Unto thy seed have I given this land, from the river of Egypt unto the great river, the river Euphrates:
Contradiction with Deuteronomy 2:9
Joshua 13:20 refers to areas within Moab allocated to Israel, whereas Deuteronomy 2:9 states that God instructed Israel not to harass Moab or engage them in battle, as He had given Ar to the descendants of Lot.
Deuteronomy 2:9: And the LORD said unto me, Distress not the Moabites, neither contend with them in battle: for I will not give thee of their land [for] a possession; because I have given Ar unto the children of Lot [for] a possession. [Distress...: or, Use no hostility against Moab]
Contradiction with Judges 11:24
Joshua 13:20 assigns land to Reuben from Moab, whereas Judges 11:24 portrays Jephthah acknowledging that Israel did not take land from Moab or Ammon.
Judges 11:24: Wilt not thou possess that which Chemosh thy god giveth thee to possess? So whomsoever the LORD our God shall drive out from before us, them will we possess.
Contradiction with 2 Chronicles 20:10
Joshua 13:20 lists cities within Moabite territory, while 2 Chronicles 20:10 notes that Israel did not invade Moab when coming from Egypt.
2 Chronicles 20:10: And now, behold, the children of Ammon and Moab and mount Seir, whom thou wouldest not let Israel invade, when they came out of the land of Egypt, but they turned from them, and destroyed them not;
Contradiction with Isaiah 15:1
Joshua 13:20 describes Heshbon and associated towns as Israelite land, Isaiah 15:1 describes a prophecy against Moab and mentions Heshbon as a Moabite city subjected to ruin.
Isaiah 15:1: The burden of Moab. Because in the night Ar of Moab is laid waste, [and] brought to silence; because in the night Kir of Moab is laid waste, [and] brought to silence; [brought...: or, cut off]