diff --git a/app/api/__init__.py b/app/api/__init__.py
index 1bc5875..decbab6 100644
--- a/app/api/__init__.py
+++ b/app/api/__init__.py
@@ -43,12 +43,13 @@ app.add_route(s_api_v1_blockchain_send_purchase_content_message, "/api/v1/blockc
 @app.exception(BaseException)
 async def s_handle_exception(request, exception):
     response_buffer = response.json({"error": "An internal server error occurred"}, status=500)
-    response_buffer = await close_db_session(request, response_buffer)
-
     try:
         raise exception
+    except AssertionError as e:
+        response_buffer = response.json({"error": str(e)}, status=400)
     except BaseException as e:
         make_log("sanic_exception", f"Exception: {e}" + '\n' + str(traceback.format_exc()), level='error')
 
+    response_buffer = await close_db_session(request, response_buffer)
     return response_buffer
 
diff --git a/app/api/routes/_blockchain.py b/app/api/routes/_blockchain.py
index 2c50ce3..d976c6b 100644
--- a/app/api/routes/_blockchain.py
+++ b/app/api/routes/_blockchain.py
@@ -5,12 +5,13 @@ from datetime import datetime, timedelta
 
 def valid_royalty_params(royalty_params):
     assert sum([x['value'] for x in royalty_params]) == 10000, "Values of royalties should sum to 10000"
-    for field_key, field_value in {
-        'address': lambda x: isinstance(x, str),
-        'value': lambda x: (isinstance(x, int) and 0 <= x <= 10000)
-    }.items():
-        assert field_key in royalty_params, f"No {field_key} provided"
-        assert field_value(royalty_params[field_key]), f"Invalid {field_key} provided"
+    for royalty_param in royalty_params:
+        for field_key, field_value in {
+            'address': lambda x: isinstance(x, str),
+            'value': lambda x: (isinstance(x, int) and 0 <= x <= 10000)
+        }.items():
+            assert field_key in royalty_param, f"No {field_key} provided"
+            assert field_value(royalty_param[field_key]), f"Invalid {field_key} provided"
     return True