There are two options for you:
1 - You may want to take a look at Lifecycle Lists (link here on a basic introduction on what they are - https://docs.airship.com/tutorials/audience/csv-list-download/) as the "set up a push notification for users who have opened the app for the first time, or even just organically opened the app in the last 7 days, 30 days, or even just yesterday" is default options that are already handled by this functionality.
2 - If you are already filtering your audience on the backend, you can then generate the list of users you want to send a push to (link here on how to create the list - https://docs.airship.com/tutorials/audience/uploaded-list/) and either upload it to the dashboard (link here on uploading the list - https://docs.airship.com/tutorials/audience/uploaded-list/) or use the API to upload the CSV and update the list as needed (links on how to upload to the API and update here - https://docs.airship.com/api/ua/#operation/api/lists/post, https://docs.airship.com/api/ua/#operation/api/lists/name/csv/put).
Please note that the Message Center doesn't exist for Web users.
Chilun Liu Senior Technical Support Engineer
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