diff --git a/src/ApiResource/ContactApi.php b/src/ApiResource/ContactApi.php
index 7311c81..5b0bd9c 100644
--- a/src/ApiResource/ContactApi.php
+++ b/src/ApiResource/ContactApi.php
@@ -62,7 +62,7 @@ class ContactApi
     #[NotBlank]
     public ?PartnerApi $partner = null;
 
-    public ?\DateTimeInterface $birthday = null;
+    public ?string $birthday = null;
 
     public ?MediaObject $image = null;