Update documentation/API-design-guidelines.md

Co-authored-by: Pedro Díez García <pedro.diezgarcia@telefonica.com>

documentation/API-design-guidelines.md

@@ -1315,7 +1315,7 @@ The Following table provides `/subscriptions` attributes
 | subscriptionExpireTime | string - date-time| Date when the event subscription should end. Provided by API requester. The Server may reject the subscription if the period requested do not comply with Telco Operator policies (i.e. to avoid unlimited time subscriptions). In this case server returns exception 403 "SUBSCRIPTION_PERIOD_NOT_ALLOWED" | optional |
 | startsAt | string - date-time| Date when the event subscription will begin/began. This attribute must not be present in the `POST` request as it is provided by API server. It must be present in `GET` endpoints | optional |
 | expiresAt | string - date-time| Date when the event subscription will expire. This attribute must not be present in the `POST` request as it is provided by API server.  | optional |
-| subscriptionMaxEvents | integer | Identifies the maximum number of event reports to be generated - Once this number reached, the subscription ends | optional |
+| subscriptionMaxEvents | integer | Identifies the maximum number of event reports to be generated (>=1) - Once this number is reached, the subscription ends | optional |
 | subscriptionDetail | object | Object defined for each event subscription depending on the event - it could be for example the ueID targeted by the subscription | optional |