Updates subscription feeds docs

openapi/index.yaml

@@ -289,12 +289,24 @@ paths:
       operationId: getSubscriptionsFeedForDate
       summary: Get Subscriptions Feed
       description:  |-
-        Returns the hashed fiscal codes of users that subscribed to or
-        unsubscribed from your service on the provided date (UTC). By querying
-        this feed on each day, you can know what users you can or cannot send
-        messages to without having to query `getProfile` for each message.
-        This is an optimization for services that send hi volumes of
-        messages per day to avoid having to make two API calls for each message.
+        Returns the **hashed fiscal codes** of users that **subscribed to** or
+        **unsubscribed from** your service **on the provided date** (UTC).
+
+        By querying this feed on each day, you will be able to retrieve the
+        "delta" of users that subscribed and unsubscribed fom your service.
+        You will have to keep a list of users somewhere in your infrastructure
+        that you will update each day by adding the subscribed users and
+        removing the unsunbscribed users.
+
+        You will then be able to query this local list to know which users you
+        can send messages, to without having to query `getProfile` for each message.
+
+        To avoid sharing the citizens fiscal codes, the API will
+        provide the hex encoding of the SHA256 hash of the upper case fiscal code.
+        In pseudo code `CF_HASH = LOWERCASE(HEX(SHA256(UPPERCASE(CF))))`.
+
+        Note that this is an optimization for those services that need to send very high
+        volumes of messages per day, to avoid having to make two API calls for each message.
       responses:
         '200':
           description: Found.