diff --git a/code/API_definitions/number-verification.yaml b/code/API_definitions/number-verification.yaml
index 6e3387b..af0c60d 100644
--- a/code/API_definitions/number-verification.yaml
+++ b/code/API_definitions/number-verification.yaml
@@ -171,17 +171,17 @@ components:
       in: header
       description: Correlation id for the different services
       schema:
-        type: string
-        pattern: ^[a-zA-Z0-9-]{0,55}$
-        example: "b4333c46-49c0-4f62-80d7-f0ef930f1c46"
+        $ref: "#/components/schemas/XCorrelator"
   headers:
     x-correlator:
       description: Correlation id for the different services
       schema:
-        type: string
-        pattern: ^[a-zA-Z0-9-]{0,55}$
-        example: "b4333c46-49c0-4f62-80d7-f0ef930f1c46"
+        $ref: "#/components/schemas/XCorrelator"
   schemas:
+    XCorrelator:
+      type: string
+      pattern: ^[a-zA-Z0-9-_:;.\/<>{}]{0,256}$
+      example: "b4333c46-49c0-4f62-80d7-f0ef930f1c46"
     NumberVerificationRequestBody:
       type: object
       description: Payload to verify the phone number.
diff --git a/code/Test_Definitions/number-verification-device-phone-number-share.feature b/code/Test_Definitions/number-verification-device-phone-number-share.feature
index c0fc5e2..259958b 100644
--- a/code/Test_Definitions/number-verification-device-phone-number-share.feature
+++ b/code/Test_Definitions/number-verification-device-phone-number-share.feature
@@ -15,10 +15,9 @@ Feature: CAMARA Number Verification API, vwip - Operation phoneNumberShare
     Given the resource "/device-phone-number/vwip" as base url
     And the header "Content-Type" is set to "application/json"
     And the header "Authorization" is set to a valid access token
-    And the header "x-correlator" is set to a UUID value
+    And the header "x-correlator" complies with the schema at "#/components/schemas/XCorrelator"
     And the request body is compliant with the schema NumberVerificationRequestBody
     And the response body is compliant with the schema NumberVerificationMatchResponse
-    And the header "x-correlator" is set to a UUID value
     And NUMBERVERIFY_SHARE_PHONENUMBER1 is compliant with the schema DevicePhoneNumber
     And NUMBERVERIFY_SHARE_PHONENUMBER2 is compliant with the schema DevicePhoneNumber
     And NUMBERVERIFY_SHARE_PHONENUMBER1 is different to NUMBERVERIFY_SHARE_PHONENUMBER2
diff --git a/code/Test_Definitions/number-verification-verify.feature b/code/Test_Definitions/number-verification-verify.feature
index 7846a2d..6452ea3 100644
--- a/code/Test_Definitions/number-verification-verify.feature
+++ b/code/Test_Definitions/number-verification-verify.feature
@@ -17,10 +17,9 @@ Feature: CAMARA Number Verification API, vwip - Operation phoneNumberVerify
     Given the resource "/number-verification/vwip"  as  base url
     And the header "Content-Type" is set to "application/json"
     And the header "Authorization" is set to a valid access token
-    And the header "x-correlator" is set to a UUID value
+    And the header "x-correlator" complies with the schema at "#/components/schemas/XCorrelator"
     And the request body is compliant with the schema NumberVerificationRequestBody
     And the response body is compliant with the schema NumberVerificationMatchResponse
-    And the header "x-correlator" is set to a UUID value
     And NUMBERVERIFY_VERIFY_MATCH_PHONENUMBER1 is compliant with the schema DevicePhoneNumber
     And NUMBERVERIFY_VERIFY_MATCH_PHONENUMBER2 is compliant with the schema DevicePhoneNumber
     And NUMBERVERIFY_VERIFY_MATCH_PHONENUMBER1 is different to NUMBERVERIFY_VERIFY_MATCH_PHONENUMBER2