Convert amount to float before adding in total calculation

handler/transactions.py

@@ -604,7 +604,7 @@ class Transactions(object):
             if not contact["data"]["is_selling"]:
                 continue
             if currency == "USD":
-                cumul_usd += amount
+                cumul_usd += float(amount)
             else:
                 rate = rates[currency]
                 amount_usd = float(amount) / rate