diff --git a/lib/lago/api/resources/event.rb b/lib/lago/api/resources/event.rb
index 330d77a..ef4b118 100644
--- a/lib/lago/api/resources/event.rb
+++ b/lib/lago/api/resources/event.rb
@@ -48,7 +48,6 @@ def whitelist_estimate_params(params)
           {
             root_name => {
               code: params[:code],
-              external_customer_id: params[:external_customer_id],
               external_subscription_id: params[:external_subscription_id],
               properties: params[:properties],
             }.compact,
diff --git a/spec/factories/event.rb b/spec/factories/event.rb
index 7f453c0..eadf726 100644
--- a/spec/factories/event.rb
+++ b/spec/factories/event.rb
@@ -28,7 +28,6 @@
   end
 
   factory :estimate_fees_event, class: OpenStruct do
-    external_customer_id { '5eb02857-a71e-4ea2-bcf9-57d8885990ba' }
     external_subscription_id { '5eb02857-a71e-4ea2-bcf9-57d8885990ba' }
     code { '123' }
     properties do