Hello @liban, please share your store URL.
Congratulations on launching your store and getting your first sale, @liban!
Regarding the fulfillment being declined, I recommend getting in touch with the app developer to clarify what happened. DSers has an email address and "Get support" option on their Shopify App Store page, or you can head to Apps > Get support in your admin to contact them.
The community would be happy to review your store and provide some feedback here if you can share the link to the store. It'd also be good to know how long the store has been open and what types of marketing you've engaged with so far to bring customers to the store. In the meantime, check out these resources for boosting traffic and driving sales: