Marketo Rest API - Bulk Lead Import - Help Request

Starting Point: https://developers.marketo.com/rest-api/bulk-import/bulk-lead-import/

We've managed to create an SSIS package dealing with the export of data from Marketo via the Bulk Lead Export. However we are struggling to import data back into Marketo via the bulk lead import API.

We are using a special component in SSIS made by Zappysys and their documentation seems to indicate this should work, however no matter what we try we're not getting any success.

Zappysys doc for multipart/form-data - https://zappysys.com/blog/rest-api-file-upload-using-ssis-multi-part-post/#Method2_8211_Upload_files_using_Multi-Part_Form_Data_mode_Mixed_content_multiple_files

We have tried every combination of content type, request data (including variable, direct file, File1= and File1.Content-Type = ) to no avail. Can anyone suggest a way to achieve this staying within SSIS (can be done with a Script Task but we'd rather avoid that)

Please let us know if we can provide any further information on this issue, and I appreciate the time anyone spends reading this.

Regards.