How to attach expense Receipts to an expense report using REST API

Hello team,

We are working on a product where user can attach expense receipts relating to an expense report through REST services. As per Oracle standard document(https://docs.oracle.com/en/cloud/saas/financials/21a/farfa/op-expensereports-expensereportsuniqid-child-expense-expenseuniqid-child-attachments-post.html), it is mentioned to use below Json format as body.

"Attachments":[
		{
			"DatatypeCode":"File",
			"Url":"http:Yahoo.com",
			"CategoryName":"Receipts",
			"FileName":"TD.txt",
			"FileContents":"JKJKJKJKJKJKJKJKJKJKJ",
			"Title":"TESTY",
			"Description":"HEKKY"
		}

I tried by using the same format and tested in Postman but attachment is not uploaded successfully. Could you please help us what details we need to give for each value type. for Eg: Url.