How are video game developers able to add integrated online stores in their games that also connect with their website online store? Like how is this done?

Ie games like Drakensang Online, Guardians of Ember, Royal Quest

Like how do they put integrated online stores into their games


I didn't find the right solution from the Internet.

References: https://www.gamespot.com/forums/game...es-33400471/#5

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