diff --git a/WultraMobileTokenSDK/Operations/Model/Requests/WMTRejectionData.swift b/WultraMobileTokenSDK/Operations/Model/Requests/WMTRejectionData.swift
index 8fab115..df5df5e 100644
--- a/WultraMobileTokenSDK/Operations/Model/Requests/WMTRejectionData.swift
+++ b/WultraMobileTokenSDK/Operations/Model/Requests/WMTRejectionData.swift
@@ -23,10 +23,10 @@ class WMTRejectionData: Codable {
     let id: String
     
     /// Rejection reason
-    let reason: WMTRejectionReason
+    let reason: String
     
     init(operationId: String, reason: WMTRejectionReason) {
         self.id     = operationId
-        self.reason = reason
+        self.reason = reason.serialized
     }
 }
diff --git a/WultraMobileTokenSDK/Operations/Model/WMTRejectionReason.swift b/WultraMobileTokenSDK/Operations/Model/WMTRejectionReason.swift
index f18fe1a..8617869 100644
--- a/WultraMobileTokenSDK/Operations/Model/WMTRejectionReason.swift
+++ b/WultraMobileTokenSDK/Operations/Model/WMTRejectionReason.swift
@@ -17,11 +17,24 @@
 import Foundation
 
 /// Reason why the operation will be rejected
-public enum WMTRejectionReason: String, Codable {
-    /// User don't want to provide the reason.
-    case unknown = "UNKNOWN"
+public enum WMTRejectionReason {
+    /// User doesn't want to provide the reason.
+    case unknown
     /// Operation data does not match (for example when user found a typo or other mistake)
-    case incorrectData = "INCORRECT_DATA"
+    case incorrectData
     /// User didn't started this operation
-    case unexpectedOperation = "UNEXPECTED_OPERATION"
+    case unexpectedOperation
+    /// Represents a custom reason for rejection, allowing for flexibility in specifying rejection reasons.
+    /// - Parameter reason: A string describing the custom rejection reason, e.g., `POSSIBLE_FRAUD`.
+    case custom(_ reason: String)
+    
+    /// Returns a string representation of the rejection reason suitable for serialization.
+    var serialized: String {
+        return switch self {
+        case .unknown: "UNKNOWN"
+        case .incorrectData: "INCORRECT_DATA"
+        case .unexpectedOperation: "UNEXPECTED_OPERATION"
+        case .custom(let reason): reason
+        }
+    }
 }
diff --git a/WultraMobileTokenSDKTests/NetworkingObjectsTests.swift b/WultraMobileTokenSDKTests/NetworkingObjectsTests.swift
index f02018e..3406c81 100644
--- a/WultraMobileTokenSDKTests/NetworkingObjectsTests.swift
+++ b/WultraMobileTokenSDKTests/NetworkingObjectsTests.swift
@@ -337,10 +337,10 @@ class NetworkingObjectsTests: XCTestCase {
     func testOperationRejectionRequest() {
         
         let expectation = """
-                          {"requestObject":{"id":"95e51995-fa60-4018-bd87-43a58f098570","reason":"UNEXPECTED_OPERATION"}}
+                          {"requestObject":{"id":"95e51995-fa60-4018-bd87-43a58f098570","reason":"COMPLETELLY_CUSTOM_REJECT_REASON"}}
                           """
         
-        let request = WMTOperationEndpoints.Reject.EndpointType.RequestData(.init(operationId: "95e51995-fa60-4018-bd87-43a58f098570", reason: .unexpectedOperation))
+        let request = WMTOperationEndpoints.Reject.EndpointType.RequestData(.init(operationId: "95e51995-fa60-4018-bd87-43a58f098570", reason: .custom("COMPLETELLY_CUSTOM_REJECT_REASON")))
         request.testSerialization(expectation: expectation)
     }
     
diff --git a/docs/Using-Operations-Service.md b/docs/Using-Operations-Service.md
index 9740dc2..304f6be 100644
--- a/docs/Using-Operations-Service.md
+++ b/docs/Using-Operations-Service.md
@@ -194,7 +194,7 @@ func approveWithBiometry(operation: WMTOperation) {
 
 ## Reject an Operation
 
-To reject an operation use `WMTOperations.reject`. Operation rejection is confirmed by possession factor so there is no need for creating  `PowerAuthAuthentication` object. You can simply use it with the following example.
+To reject an operation use `WMTOperations.reject`. Operation rejection is confirmed by a possession factor, so there is no need for creating a `PowerAuthAuthentication` object. You can simply use it with the following example.
 
 ```swift
 import WultraMobileTokenSDK