Within the Pango app, go to your account menu and select "My Notification Settings." On this page, you can opt-out of any sort of notification including when sellers you follow offer a special discount.
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If you'd like to stop receiving notifications from a specific shop altogether, simply navigate to the seller's main shop page. Next to the button that says “Following” you’ll see a small bell icon. Clicking this toggles whether or not you receive notifications from this seller. When you follow a seller, the button will be enabled by default, but you can disable notifications from them at any time by tapping the bell.