[TELE-636] fix json loading by decoding bytes var

passerelle_imio_extra_fees/models.py

@@ -57,7 +57,7 @@ class ExtraFees(BaseResource):
     def default_compute(self, request, **kwargs):
         nb_documents = 0
         nb_letter = 0
-        data = json.loads(request.body)
+        data = json.loads(request.body).decode('utf-8')
         postage_fee = Decimal(self.belgium_postage_fee)
         for basket_item in data['data']:
             try: