> ## Documentation Index
> Fetch the complete documentation index at: https://www.plain.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# addCustomerToCustomerGroups

> Add a customer to one or more customer groups (up to 25 at once), identified by group ID, key, or external ID. Memberships that already exist are silently skipped, making this operation safe to call repeatedly. Returns only the newly created memberships. Requires `customerGroupMembership:create` permission.