API Create Invoice

Can someone point me to the issue causing this error?

Posting to /api/documents?company_id=ABC&search=type:invoice"
with the appropriate headers.
I'm using c# and posting using MultipartFormDataContent.

"message": "SQLSTATE[22007]: Invalid datetime format: 1366 Incorrect integer value: '''' for column `akaunting`.`zun_document_items`.`item_id` at row 1 (SQL: insert into `zun_document_items` (`company_id`, `type`, `document_id`, `item_id`, `name`, `description`, `quantity`, `price`, `tax`, `discount_rate`, `total`, `updated_at`, `created_at`) values (1, invoice, 33, '', ITEM, total weight and volume based, 149.38, 1.73, 0, 0, 258.43, 2021-08-13 00:07:48, 2021-08-13 00:07:48))"