in php, How can I extract a JSON from an array?

I'm receiving a string from the database and I only want to use the JSON so I can use a json_decode on it.

this is the string:

array(1) { [0]=> array(4) { ["reporte_id"]=> int(1) ["tabla_id"]=> int(1) ["configuracion"]=> string(1000) "{"tabla":"servtp","config":[{"name":"Client","type":"smallint","notnull":"0","pk":"0"},{"name":"Distribuidor_","type":"varchar(40)","notnull":"0","pk":"0"},{"name":"Branch","type":"smallint","notnull":"0","pk":"0"},{"name":"Cve","type":"smallint","notnull":"0","pk":"0"},{"name":"FechaApertura","type":"date","notnull":"0","pk":"0"},{"name":"FechaFactura","type":"date","notnull":"0","pk":"0"},{"name":"Dias","type":"smallint","notnull":"0","pk":"0"},{"name":"WorkingDays","type":"real","notnull":"0","pk":"0"},{"name":"Mes_","type":"smallint","notnull":"0","pk":"0"},{"name":"NumeroOT","type":"varchar(10)","notnull":"0","pk":"0"},{"name":"VentasNetas_","type":"real","notnull":"0","pk":"0"},{"name":"TipoOrden","type":"varchar(30)","notnull":"0","pk":"0"},{"name":"Type","type":"varchar(3)","notnull":"0","pk":"0"},{"name":"Taller","type":"varchar(30)","notnull":"0","pk":"0"},{"name":"Clasificacion_","type":"varchar(16)","notnull":"0","pk":"0"},{"name":"Retencion_","type":"varchar(1)","notnull":" ["nom_reporte"]=> string(33) "Monthly Service Operation Report " } }