diff --git a/src/WalletFramework.Oid4Vc/Oid4Vp/PresentationExchange/Models/PresentationDefinition.cs b/src/WalletFramework.Oid4Vc/Oid4Vp/PresentationExchange/Models/PresentationDefinition.cs
index 3657bb5..f922016 100644
--- a/src/WalletFramework.Oid4Vc/Oid4Vp/PresentationExchange/Models/PresentationDefinition.cs
+++ b/src/WalletFramework.Oid4Vc/Oid4Vp/PresentationExchange/Models/PresentationDefinition.cs
@@ -36,6 +36,7 @@ public class PresentationDefinition
     /// <summary>
     ///     This MUST be a string that describes the purpose for which the Presentation Definition's inputs are being used for.
     /// </summary>
+    [JsonProperty("purpose")]
     public string? Purpose { get; }
 
     /// <summary>