Hello @MayankShoree,

I think it would help the rest of the Community if you were able to share the call you’re making and/or provide the exact endpoint you’re hitting. Typically, if you were looking to bulk import profiles to a Klaviyo list, this is accomplished by making a POST request to the https://a.klaviyo.com/api/v2/list/{list_id}/members endpoint. As mentioned in the Add Members to a List Developers portal, making requests to this endpoint is functionally equivalent to adding profiles to a list via a CSV upload and will immediately add profiles to the list.

Since it sounds like you already have an existing list of contacts/profiles you were looking to bring to Klaviyo, rather than using API, importing these contacts/profiles via a .CSV would accomplish the same thing as adding users in bulk through the API. The benefit of importing a large number of contacts via a .CSV versus the API is that you would not be restricted to the endpoint’s rate limit. You can learn more about importing contacts to Klaviyo using a .CSV from the How to Add Subscribers to an Existing List and How to Create and Add Contacts to a New List Help Center articles.

I hope this helps!

David