Unable to set CC Expiration Date using SS2.0

I'm currently trying to set a customer's credit card via SS2.0 and getting stuck:

Looping through an object to set the fields with their associated field values yields:

{    "type": "error.SuiteScriptError",    "name": "USER_ERROR",    "message": "Please enter a valid expiration date",    "stack": [      "anonymous(N/recordService)",      "doPost(Script.js:207)"    ],    "cause": {      "type": "internal error",      "code": "USER_ERROR",      "details": "Please enter a valid expiration date",      "userEvent": null,      "stackTrace": [        "anonymous(N/recordService)",        "doPost(Script.js:207)"      ]    },    "id": ""  }

and the credit card object looks like:

    "creditcards": {        "0": {      "ccname": "Test CC Name",      "ccnumber": "",      "ccexpiredate": "6/2020",      "paymentmethod": 6        }      },

or

    "creditcards": {        "0": {      "ccname": "Test CC Name",      "ccnumber": "",      "expmonth": "06",      "expyear": "2020",      "paymentmethod": 6        }      },

nor

    "creditcards": {        "0": {      "ccname": "Test CC Name",      "ccnumber": "",      "expmonth": "6",      "expyear": "2020",      "paymentmethod": 6        }      },