OptionaldataApplication data delivered together with the message, for the receiving app to know what the notification
refers to; it doesn't change what the device shows. The values must be strings: FCM refuses anything else
inside its data block. Ignored when json is set.
The endpoint of the notification.
OptionaljsonIf set, message and platform will be ignored and the content of this attribute will be preferred.
OptionalmessageThe message to send.
OptionalplatformThe platform receiver; used to structure the message.
Options to publish a message on a SNS endpoint.