I am using 5.6.
At line 25-36 in the OnlineSubsystemGooglePlay_UPL.xml file I see:
<!-- gradle dependencies additions -->
<buildGradleAdditions>
<if condition="bSupportsInAppPurchasing">
<true>
<insert>
dependencies {
implementation 'com.android.billingclient:billing:7.1.1'
}
</insert>
</true>
</if>
</buildGradleAdditions>
Looking at the github commit (https://github.com/EpicGames/UnrealEngine/commit/2e857ed523d275a9ec22917080810ef0edbe729e) it was updated ~2 months ago