%ToJson not working

Hello Gabriel, you can use the% ZEN classes, as the example below:

ClassMethod ConvertJSON() As %Status
{
Set tSC = $$$OK
    Try{
    
    Set Store  = ##class(%ZEN.proxyObject).%New(),
    Clients = ##class(%ListOfObjects).%New(),
    Client  = ##class(%ZEN.proxyObject).%New()     Set Client.code = 1,
   Client.name = "Leonardo"
Do Clients.Insert(Client)
   
    Set Store.name = "Intersystems Store",
    Store.address = "80 Delancey St, New York, NY",
    Store.clients = Clients
   
   $$$THROWONERROR(tSC, ##class(%ZEN.Auxiliary.jsonProvider).%WriteJSONStreamFromObject(.JsonStore,Store))
   Write JsonStore.Read()
       
} Catch tException {
Set:$$$ISOK(tSC) tSC = tException.AsStatus()
    }
    Quit tSC
}