Error when using vsnprintf

I am playing around with mbed-os-example-aws-iot-client, which I have imported into my mbed workspace. I am using the CY8CKIT-062-WIFI-BT board, though I don’t think that’s relevant. When I try and use vsnprintf(), vsprintf(), sprintf() or any variations, I get
Error: No matching function for call to 'vsprintf' in "mbed-os-example-aws-iot-client/publisher/publisher.cpp", Line: 118, Col: 9
However, all the resources I can find say this should be part of mbed.h. I also tried including stdio.h, , etc but same result. When I put the cursor over vsnprintf() I get a little popup in the upper right hand corner showing what the arguments are, so clearly the editor knows it’s a function and even knows its definition.
Any help would be greatly appreciated!