How do I do a property transfer with multiple source responses into one target?

Unfortunately, do not have environment to try that property transfer to get it work.

What i see is you will be able to access the values from first Json response

change from 

[token_type, access_token]

to

add two properties in Property transfer step

prop1 -> $.token_type

prop2->  $.access_token

But the problem is each one goes to different target.

For now, the below solution should be helpful

Disable property transfer step.

Add the script assertion with following code for the first rest step

import net.sf.json.groovy.JsonSlurper
def jsonSlurper = new JsonSlurper()
def object = jsonSlurper.parseText(messageExchange.responseContent)
def accessToken = object.access_token
def tokenType = object.token_type
assert null != accessToken, "access_token does not have a value"
assert null != tokenType, "token_type does not have a value"
def authorizationKey = "${tokenType} ${accessToken}"
context.testCase.setProperty('AUTH_KEY',authorizationKey)

Now in the second step, use ${#TestCase#AUTH_KEY} where the value is required.