diff --git a/lib/lago/api/resources/customer.rb b/lib/lago/api/resources/customer.rb
index 9196a54..2552d61 100644
--- a/lib/lago/api/resources/customer.rb
+++ b/lib/lago/api/resources/customer.rb
@@ -46,7 +46,7 @@ def checkout_url(external_customer_id)
             "#{client.base_api_url}#{api_resource}/#{external_customer_id}/checkout_url",
           )
 
-          response = connection.post(uri)[root_name]
+          response = connection.post({}, uri)[root_name]
 
           JSON.parse(response.to_json, object_class: OpenStruct)
         end
diff --git a/spec/lago/api/resources/customer_spec.rb b/spec/lago/api/resources/customer_spec.rb
index 07c9e29..2b3bd4f 100644
--- a/spec/lago/api/resources/customer_spec.rb
+++ b/spec/lago/api/resources/customer_spec.rb
@@ -253,11 +253,7 @@
 
     context 'when the customer exists' do
       before do
-        # NOTE: Api makes POST to /customers endpoint first
-        # stub_request(:post, "https://api.getlago.com/api/v1/customers/#{customer_external_id}/checkout_url")
-        #   .to_return(body: response_body, status: 200)
-
-        stub_request(:post, 'https://api.getlago.com/api/v1/customers')
+        stub_request(:post, "https://api.getlago.com/api/v1/customers/#{customer_external_id}/checkout_url")
           .to_return(body: response_body, status: 200)
       end
 
@@ -275,11 +271,7 @@
       let(:customer_external_id) { 'DOESNOTEXIST' }
 
       before do
-        # NOTE: Api makes POST to /customers endpoint first
-        # stub_request(:post, "https://api.getlago.com/api/v1/customers/#{customer_external_id}/checkout_url")
-        #   .to_return(body: JSON.generate(status: 404, error: 'Not Found'), status: 404)
-
-        stub_request(:post, 'https://api.getlago.com/api/v1/customers')
+        stub_request(:post, "https://api.getlago.com/api/v1/customers/#{customer_external_id}/checkout_url")
           .to_return(body: JSON.generate(status: 404, error: 'Not Found'), status: 404)
       end