So when intervention-payer-type is empty, show nothing, if it has a value, show:
PAYEUR
Type de payeur : " + 3.Type de donneur d’ordre + "
Société du payeur : " + 1.data.`Company Name```
Is that correct?
Generally, it is not needed to mix the ifempty and if functions. You can achieve the outcome with only the if function:
{{if(1.data.`intervention-payer-type` != emptystring; "PAYEUR
Type de payeur : " + 3.`Type de donneur d'ordre` + "
Société du payeur : " + 1.data.`Company Name`; null)}}