diff --git a/models/api/sms/send.py b/models/api/sms/send.py
index 05b0e73..b24c770 100644
--- a/models/api/sms/send.py
+++ b/models/api/sms/send.py
@@ -153,10 +153,11 @@ class SavvyBulkSMSKenyaMessage(BaseModel):
 
 class SMSSendRequestHeaders(BaseModel):
 
-    sessionToken: str = Field(
+    sessionToken: str | None = Field(
         description = "the session token of the user who is requesting the service",
         pattern = REGEX_SESSION_TOKEN,
         frozen = True,
+        default = None,
         alias = "X-Session-Token"
     )