Hello!
ShipStation should be importing your orders with all the available order data for the specific store integration you are using, and its default behavior is to notify the marketplace once you've shipped the order (that is, once you've created the label). Is this not occurring? If not, what selling channel are you importing orders from? Is it not importing all the data? or is it not sending the notification back to the marketplace?
To send shipment notification emails to the customer, you must set the Notifications options in each of your store's Store Settings in ShipStation to do so. Go to Settings > Selling Channels > Store Setup, then click Edit next to your store. Then click the Notifications tab and select the email template you want to use.
ShipStation will send the shipment notification based on the settings you set in this screen. These must be set for each store you want to send notifications from.
The tracking number associated with the label will be sent in both the email and the marketplace notification automatically. If you are instead building either a custom store or using ShipStation's openAPI, you'll need your developer to review the related documentation for each, which will tell you how to get the data you need for the API calls you are making.
