Pipeline Webhook, Can't add a File to do a 3rd Party API Call.

Hi, I'm having trouble to attach a file to perform an UpdateLookupList API call to Fastfield in my Pipeline. The requirements of this API call are: request session token, API key, file to be updated (.csv) and endpoint. I manage to get working "GetLookupList" API call since this one does not require a file with JSON Handler. How can i attach a file to use for the update?

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Gonzalo Carrasco
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