PUT on a custom object that has referenced object custom field

Hi,

Thanks in advance. I have a custom object which has a custom field that is a referenced object to Project. I'm using data/objects/C_MyCustomObject to PUT data into the custom object. 

C_MyCustomObject has 2 fields 

• C_CreatedOn (DateTime)
• C_ProjectName (Reference to Project Object)

I'm able do a PUT with just C_CreatedOn. Can someone please tell me how to PUT C_ProjectName?

Thanks

Shamin