Complex sentence: Andexanet alfa acts as a decoy receptor for Xa inhibitors meaning that it inhibits Xa inhibitors to bind to its normal receptor, factor Xa, and instead Xa inhibitors bind to Andexanet.
Split into simpler sentences: Andexanet alfa acts as a decoy receptor for Xa inhibitors. Therefore that it inhibits Xa inhibitors to bind to its normal receptor, factor Xa, and instead Xa inhibitors bind to Andexanet.