v12 REST API - Client-SSL Profile - Updating Chain

I'm getting the following error

010717e7:3: cert-key-chain and profile cert, key or chain options cannot be input together.

when attempting to update a client SSL profile with a new cert chain.

The same code worked in v11.5.x but it returns the above error in v12x.

My code sends the following JSON payload via a PUT cmd to /mgmt/tm/ltm/profile/client-ssl/(resource ID):

{"certKeyChain":[{"name":"(NAME OF CERT)","cert":"(FULL PATH TO CERT's .CRT FILE)","chain":"(FULL PATH TO CA's .CRT FILE)","key":"(FULL PATH TO CERT's .KEY FILE)"}]}

And the only part of that JSON payload I am changing is the "chain" value. I'm sending back everything else exactly the same from the GET call before the PUT.