Adding Contact to Opportunity

Hey there,

 

I am having some problems adding a new contact to an existing opportunity. 

 

The documentation indicates that the 'OtherContacts' field of the Opportunity is a "OpportunityContactArray' type, however when attempting to use that - errors indicate that it needs to be a 'OpportunityContactDeltaArray'...  I have tried several ways to add a contact to the OtherContacts field with no success:

 

 

Can you please advise where I am going wrong?

 

Thanks!