Notify user when event date is near

I am starting an application (ionic + angular + cloud firestore) and I need to notify users when a date is approaching. * (This date is different for all users and is stored in the cloud firestore) *

Example: The user has an invoice to pay by 6/20/2020 and I want to notify 15 days before the deadline. There may be the possibility of having more than one date for another event.

I wonder if that is possible. If so, I wanted to know what the best option is (push notification or local notification).

Grateful for the attention

You can write in cloud function. You need a cron job. You can calculate the remaining time and send notification according to the situation.

For example, a thread that runs at 10 o’clock every day.