Hello, I'm trying to modify specific users' subscribed lists. The problem is that I don't have their Contact ID, just their email address and other personal information. Is there a way using the API to retrieve their Contact ID by email address to update that users' subscribed lists? If I try to add the user to Contacts, the API comes back with an error that the user already exists, and in the error message, it has the users' Contact ID. I can parse the ID from the string but doesn't feel reliable, and I was hoping the API had an actually way to retrieve the Contact ID in a better / more reliable manner.
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