[Multipass] I got 'duplicated email' error when i tried to login via Multipass

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Topic summary

Issue: enabling Shopify Multipass (SSO) for existing customers while needing the Shopify customer_id to sync an external DB.

Key constraints: Multipass login doesn’t return customer_id. The poster created a new customer via the Admin API with a multipass_identifier to obtain customer_id.

Errors encountered: Logging in via Multipass with the identifier triggers a “duplicated email” error. Attempting login without providing an email results in a “no email” error.

Guidance cited: Shopify’s docs state to set the multipass_identifier on the existing customer via the Customer API and use that identifier in all Multipass requests (i.e., map external identities to existing Shopify customer records).

Requests/links: One reply asks for a code sample to diagnose the issue. Another provides a related community thread link about multipass_identifier.

Status: Unresolved. No confirmed workaround or fix yet. Next steps are to share code for debugging and review the linked resource. Core open question: how to configure Multipass for existing Shopify customers without creating duplicates or email conflicts.

Summarized with AI on December 23. AI used: gpt-5.
1

I need ‘customer_id’ to synchonize our DB and Shopify Data. And Also I have to use Shopify’s Multipass.

But There is no way to get ‘customer_id’ via Shopify’s Multipass Login.

So I tried to create new register via Shopify Admin API with multipass_identifier, and got ‘customer_id’.

And then I tried to login via Shopify’s Multipass with identifier. As a result, I got a error which is ‘duplicated email’.

If I tried to login via Shopify’s Multipass without email, I got a error that there is no email.

In Multipass Login Guide,

Some of my customers have already placed orders on Shopify. How do I update those customers so they can login through multipass?

You can use the Customer API to set the multipass_identifier for the customer. You will need to use the identifier with all your multipass requests for those customer accounts

How to use Multipass login with existing customer???

2

Hey @WhosfanStore

Can you provide a code example of where you get stuck?

3

This might help:
https://community.shopify.com/post/2690617