Specifying functions responses

When using functions, when I specify a function the assistant will not continue if the for is as follows:

{‘success’: ‘true’, ‘resources’: …

however if the response is slightly altered, even to (changing the first quote from single (') to double (") quotes :

{"success’: ‘true’,…

then the assistant is happy to move on. I am assuming this isnt by design? And if it is, can someone offer advice on how best to format function call responses?