From Seller Portal, you can add a Samsung In-App Purchase (IAP) product (item or subscription). See also Creating an In-App Product
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Go to the app list and open an app.
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Select the In-App Purchase tab and click Add New Product.

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Click Item.

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Enter the Product ID, Product Title, and Description of your item and click Next. All basic information must be entered in English.

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Click Set New Price

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Enter a standard price (in USD) for all countries and click Apply. Or, set a price for each country (in the local currency). You can also connect a price template, which allows you to set a fixed local price in each country where your app is sold and can be applied to one or more in-app products of an app.

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When you have entered the price, click Save then click Next.
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Review the information you have just entered and click Save then OK.
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Activate your item: select the checkbox next to the item you just added, then click Activate and OK.

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Go to the app list and open an app.
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Select the In-App Purchase tab and click Add New Product.

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Click Subscription.

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Enter the Product ID, Product Title, and Description of your item and click Next. All basic information must be entered in English.

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Click Set New Price

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Enter a standard price (in USD) for all countries and click Apply. Or, set a price for each country (in the local currency). You can also connect a price template, which allows you to set a fixed local price in each country where your app is sold and can be applied to one or more in-app products of an app.

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When you have entered the price, click Save. If you want to add an introductory price, select the checkbox then click Set New Discounted Price and enter the Discount Period.
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Click Next and select the Payment Cycle. You can also add a grace period and free trial period.

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Click Next and review the information you have just entered. Then click Save and OK.
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Activate your subscription: select the checkbox next to the subscription you just added, then click Activate and OK.