In Revenue Cat, I can't retrieve a modified user id

Hello everyone,
When a user registers in my app, I create an account for them on the Revenue Cat platform with a POST call to this url https://api.revenuecat.com/v2/projects/projxxxxxx/customers. I ask for the creation of a new customer and I also ask for app_user_id RevenueCat to be the unique identifier that my user has in my app so that I can find him easily when he is in RC.
When I go to “customers” in R C, my customer is there, with the app_user_id set to the unique identifier in the app.
So so far so good!
Except that when my user takes out a subscription on app, Revenue cat creates a new Revenue Cat identifier for him, whereas I want the customer to keep his app_user_id identical to the unique identifier in my app.

The app_user_id is updated in RevenueCat? Should this field be set to the unique_id of the User in Bubble and therefore not ever change?

Are you somehow passing a new value for the app_user_id in the subscribing action API call?

I’d have a look at whatever endpoint you are using and see what it exactly does.

Thanks for your help.

The app_user_id is updated in RevenueCat?
Yes

Should this field be set to the unique_id of the User in Bubble and therefore not ever change?
Yes

Just before my payment (via the webtonative plugin) I make this Post call to tell RC that I want this unique id of my Bubble user that you RC have in your Revenue Cat customers.
Are you somehow passing a new value for the app_user_id in the subscribing action API call?
Yes I pass the value “Current user’s unique id ”.