diff --git a/app/models/callout_participation.rb b/app/models/callout_participation.rb
index 42630034d..3860a6571 100644
--- a/app/models/callout_participation.rb
+++ b/app/models/callout_participation.rb
@@ -32,6 +32,13 @@ def self.still_trying(max_phone_calls)
     where(answered: false).where(arel_table[:phone_calls_count].lt(max_phone_calls))
   end
 
+  # NOTE: This is for backward compatibility until we moved to the new API
+  def as_json(*)
+    result = super
+    result["msisdn"] = result.delete("phone_number")
+    result
+  end
+
   private
 
   def set_phone_number_from_contact
diff --git a/app/models/contact.rb b/app/models/contact.rb
index 551a325f8..66a6051ac 100644
--- a/app/models/contact.rb
+++ b/app/models/contact.rb
@@ -31,7 +31,7 @@ def self.jsonapi_serializer_class
   # NOTE: This is for backward compatibility until we moved to the new API
   def as_json(*)
     result = super
-    result["msisdn"] = result["phone_number"]
+    result["msisdn"] = result.delete("phone_number")
     result
   end
 end
diff --git a/app/models/phone_call.rb b/app/models/phone_call.rb
index 223e6d22a..0071dc1f2 100644
--- a/app/models/phone_call.rb
+++ b/app/models/phone_call.rb
@@ -140,7 +140,7 @@ def remote_call_expired?
   # NOTE: This is for backward compatibility until we moved to the new API
   def as_json(*)
     result = super
-    result["msisdn"] = result["phone_number"]
+    result["msisdn"] = result.delete("phone_number")
     result
   end