Your command is wrong must edit like this
If you need to sum number you must add number in command
{
“Name”: “merge”,
“CreationDate”: “2020-11-27”,
“Commands”: [
{
“Command”: “store”,
“Target”: “home”,
“Value”: “mois”
},
{
“Command”: “executeScript_Sandbox”,
“Target”: “return (0 + ${mois})”,
“Value”: “mois”
}
]
}