Hi Adrian,
Could you confirm if my understanding is correct that what you are looking for is a way via the Google Ads API to add a list of emails into your existing userlists? If yes, then, adding members to your userlists is currently not supported in the Google Ads API.
For now, only the AdWords API can be used to update your userlists with members using the
AdwordsUserListService.mutateMembers() method. I hope this helps.
Thanks and regards,
Peter
Google Ads API Team

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