I’m here searching for a solution since 2023 when I switched from 4.27 to 5.3.2 version, (current 5.4.4). Today I found a solution to Show External Login UI and In-App Purchases native plugins within Unreal Engine. Using the Android Native Goodies plugin. I was using it to show push notifications on Android and now simply the Show External Login UI and IAP started working, this plugin is large and has many nodes, I only used the notifications ones which increased only 1MB in my final project, I believe it injected or updated some dependency that no one knows that makes the Login and IAP on Play Store functionality stop from version 5+. So you who were looking for the light to this problem like I was since 2023 this plugin will apparently fix all of that
Unreal version 5.4.4