To set the value for the user ID, set the value with setUserID and set the value. To get the value of the user ID also in the user property You also need to set the value of ”customer_id（Our service ID）” in setUserProperty.

I read the article below　 https://firebase.google.com/docs/analytics/user-properties?platform=ios

Based on the following document, so that you can set setUserProperty from WebView I am preparing the interface on the native side, but it is not GTM, Is it okay to understand that you set the setUserProperty natively? https://firebase.google.com/docs/analytics/webview?hl=ja&platform=ios

I don't call it by the natives themselves, If it is called via WebView, it will work.

Is my understanding correct?