ZAP 2.4.1 will be released very soon (probably this week).
A random API key will now be created by default, meaning that the API calls will fail.
There are 2 options for getting around this.
One is to set the key to a known value that you use in the script using a command line option like "-config api.key=12345"
The other option is to disable use of the API key using "-config api.disablekey=true"
Note that we generally recommend against this in most situations as it can make ZAP vulnerable to attacks from malicious web sites. In this particular case the risks might be less than in other cases.