As Sezzle is an alternative payment provider outside of Shopify, they would have a documentation on how to remove their integration from Shopify stores. I've taken a look at their documentation page and they have provideduninstallation instructions here. It looks like if you've deleted the Sezzle app from your Shopify admin, you can also double check within yourAlternative Paymentspage too, to see if Sezzle has been deactivated.
If you're still seeing the Sezzle widget on your storefront after deactivating Sezzle under Alternative Payments, you can perhaps try to reinstall the Sezzle app, and follow theirinstructions under Step 4 hereon how to remove the Sezzle widget within their app. Once removed, you can uninstall the app again from your store.
It's also possible that the Sezzle integration may have left some residual codes on your store's theme, even after the steps taken above. If this is the case, you canreach out to Sezzle's teamto see if they can help remove any leftover codes that are still lingering on your theme.
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