Hey @Lukasz Kopcinski Racheal from the support engineer team here👋
A 409 means multiple existing users match this email address and you must be more specific using user_id. This typically means there is an issue with having multiple users who have the same email address, and Intercom not knowing which one you are trying to log in. So there was likely a duplicate user created with the same email and now without a User ID being present in your installation, we are unsure which user you are referring to. Before you provide the different external_id, is there an ID provided at all?
This can be fixed by archiving / deleting one of these users, or updating them to have a User ID, and then including User ID when identifying users. Note, to update a User ID in Intercom you must use the REST API. We recommend that you always include a User ID when Identifying users, as it can help mitigate issues like this in the future, read more about implementing that in the iOS SDK here 👈