How to send a push notification from an API

Greetings, i need help figuring out how to emit from outside google firebase a push notification into a device. I managed to do it manually using google firecloud messaging, however i need to do it using some sort of automation like an alarm. For example: I need the user to receive a scheduled PUSH notification every time he registers some date for him to receive a notification that the time has come. But i want him to register the date, and send it somewhere that’ll tell firebase every when to send the push notification, please, and thanks in advance.

Hello, @puelon please check this out

FCM notification not working when app is kill/closed

does that code work with OneSignal postNotification? because i found my solution by using OneSignal API, but now i need to send post notifications using jquery lol

No, One-signal is completely different plugin then FCM/Push. refer below link for the API’s of One-signal push notification and then implement your code using it.
https://documentation.onesignal.com/v5.0/reference#create-notification