diff --git a/code/API_definitions/energy-footprint-notification.yaml b/code/API_definitions/energy-footprint-notification.yaml
index 000e83c..ef7cc0d 100644
--- a/code/API_definitions/energy-footprint-notification.yaml
+++ b/code/API_definitions/energy-footprint-notification.yaml
@@ -418,7 +418,7 @@ components:
             Note: the maximum number of event types per subscription will be decided at API project level
           type: array
           minItems: 1
-          maxItems: 1
+          maxItems: 2
           items:
             $ref: "#/components/schemas/SubscriptionEventType"
         config:
@@ -427,14 +427,32 @@ components:
         propertyName: protocol
         mapping:
           HTTP: "#/components/schemas/HTTPSubscriptionRequest"
-          MQTT3: "#/components/schemas/MQTTSubscriptionRequest"
-          MQTT5: "#/components/schemas/MQTTSubscriptionRequest"
-          AMQP: "#/components/schemas/AMQPSubscriptionRequest"
-          NATS: "#/components/schemas/NATSSubscriptionRequest"
-          KAFKA: "#/components/schemas/ApacheKafkaSubscriptionRequest"
+    HTTPSubscriptionRequest:
+      allOf:
+        - $ref: "#/components/schemas/SubscriptionRequest"
+        - type: object
+          properties:
+            protocolSettings:
+              $ref: "#/components/schemas/HTTPSettings"
+    HTTPSettings:
+      type: object
+      properties:
+        headers:
+          type: object
+          description: |-
+            A set of key/value pairs that is copied into the HTTP request as custom headers.
+
+            NOTE: Use/Applicability of this concept has not been discussed in Commonalities under the scope of Meta Release v0.4. When required by an API project as an option to meet a UC/Requirement, please generate an issue for Commonalities discussion about it.
+          additionalProperties:
+            type: string
+        method:
+          type: string
+          description: The HTTP method to use for sending the message.
+          enum:
+            - POST
     Protocol:
       type: string
-      enum: ["HTTP", "MQTT3", "MQTT5", "AMQP", "NATS", "KAFKA"]
+      enum: ["HTTP"]
       description: Identifier of a delivery protocol. Only HTTP is allowed for now
       example: "HTTP"
     Config:
@@ -695,7 +713,9 @@ components:
         propertyName: "type"
         mapping:
           org.camaraproject.energy-footprint-notification.v1.energy: "#/components/schemas/CloudEventEnergy"
+          org.camaraproject.energy-footprint-notification.v1.energy.error: "#/components/schemas/CloudEventError"
           org.camaraproject.energy-footprint-notification.v1.carbon-footprint: "#/components/schemas/CloudEventCarbonFootprint"
+          org.camaraproject.energy-footprint-notification.v1.carbon-footprint.error: "#/components/schemas/CloudEventError"
     CloudEventEnergy:
       description: provides back the energy consumption for the service. The
         result of the analysis is a floating point number. The unit of measure