You can upload attachments to tasks using the ClickUp API.
View the Create Task Attachment endpoint.
Uploading attachments to ClickUp is one of the only times that you will not include
Content-Type: application/json in the header of your request. You need to send your request using
Content-Type: multipart/form-data, which varies by coding language.
If you are unfamiliar with the
multipart/form data format, check out this article.
You can use multipart/form data using Postman by following these instructions.