Steps to reproduce:

1. Execute API request to host.create method using such parameters:

   {
   	"host":"new host 1",
   	"groups":{
   		"groupid": "5"
   	},
   	"interfaces": [
   		{
   			"type": 1,
   			"main": 1,
   			"useip": 1,
   			"ip": "192.168.3.1",
   			"dns": "",
   			"port": "10050"
   		}
   	]
   }
   

Observe:
Runtime error in php log file:

Illegal string offset 'groupid' in /var/www/html/master/ui/include/classes/api/services/CHost.php on line 1984