How to write the information in Custom fields from API?

[IDev2]

Hello. Some information:

1. Iframe connected with HS db (we are getting some product information)

2. The result of the using iframe is: create line items on Deals object

The problem is: some fields on Deals object are custom.

How can I write the information in these Custom Fields from API?

[Jaycee_Lewis]

Hey, @IDev2 👋 Can you clarify things a bit for the community? Is the issue that you cannot update custom properties for a Deal record? Can you include an example of the request URL and body along with the response? 

Best,

Jaycee