By default ZAP will now also only allow connections from the local machine. You can set which IP addresses can connect to the API using the command line:
-config api.addrs.addr.name=123.456.789.123
If you are using ZAP in a completely isolated environment you can allow all IP addresses to connect to the ZAP API using:
-config api.addrs.addr.name=.* -config api.addrs.addr.regex=true
You will also need to set or disable the API key - see the FAQ: Why is an API key required by default?
If you still have problems connecting then look in the zap.log file for any
error messages as per the FAQ: Somethings not working - what should I
do?