An apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus at least to: - receive, from a first network function consumer, a subscribe request for a second network function consumer to subscribe to a service, wherein the subscribe request comprises a notification address and identifies the second network function consumer, - transmit (310, 614), to a network repository function, an access token request for an access token for requesting authorization from the second network function consumer, wherein the access token request comprises the notification address and identifies the second network function consumer, - receive, from the network repository function, an access token response comprising an access token comprising the notification address verified by the network repository function, - transmit (330, 622), to the second network function consumer, an authorization request for receiving data authorization of the second network function consumer, wherein the authorization request comprises the access token comprising the notification address and the requested data authorization comprises validation of the notification address and confirmation of willingness to accept data from the apparatus, - receive, from the second network function consumer, an authorization response indicating that the second network function consumer considers the notification address to be valid and is willing to accept data from the apparatus, and - transmit (350, 628), on the basis of the authorization response, a notification of the service to the second network function consumer. - receive, from a first network function consumer, a subscribe request for a second network function consumer to subscribe to a service, wherein the subscribe request comprises a notification address and identifies the second network function consumer, - transmit (310, 614), to a network repository function, an access token request for an access token for requesting authorization from the second network function consumer, wherein the access token request comprises the notification address and identifies the second network function consumer, - receive, from the network repository function, an access token response comprising an access token comprising the notification address verified by the network repository function, - transmit (330, 622), to the second network function consumer, an authorization request for receiving data authorization of the second network function consumer, wherein the authorization request comprises the access token comprising the notification address and the requested data authorization comprises validation of the notification address and confirmation of willingness to accept data from the apparatus, - receive, from the second network function consumer, an authorization response indicating that the second network function consumer considers the notification address to be valid and is willing to accept data from the apparatus, and - transmit (350, 628), on the basis of the authorization response, a notification of the service to the second network function consumer.