Hi @simon_Piquemal 
I enlisted @oleg 's help here, but it looks like it’s an issue with your JSON. Instead of:
{
"nom": "string",
"prenom": "string"
}
Your root part needs to be a JSON object like this:
{
"type": "object",
"properties": {
"first_name": {
"type": "string"
},
"last_name": {
"type": "string"
}
}
}
Mind you that Oleg translated this to English, so don’t be too confused 
But here’s the workflow with this fixed up:
Sneaky edit: you can also probably just connect the Output parser directly, like this:
