If you receive multiple notifications when sending out a campaign, this may be because you've subscribed to your notifications from multiple sources, besides your original domain.
When setting up your PushOwl account, you would be asked to subscribe to your store notifications. In this case, you'll be subscribing to your notifications from the dashboard.pushowl.com domain.
Similarly, if you've been previewing your store theme while editing your store design, you'll be shown a browser prompt, asking you to subscribe to your store notifications from the shopifypreview.com domain.
Since you've subscribed from different domains, you'll receive multiple notifications when sending one campaign.
But, when your customers receive your notifications, they will be shown your domain.