diff --git a/models/data/tech/alerts.py b/models/data/tech/alerts.py
index dac727e..2bf6bc1 100644
--- a/models/data/tech/alerts.py
+++ b/models/data/tech/alerts.py
@@ -73,8 +73,10 @@ REGEX_SESSION_TOKEN = r"^[a-f0-9]{8}-[a-f0-9]{4}-[1-5][a-f0-9]{3}-[89ab][a-f0-9]
 
 class ChatAlertRequestHeaders(BaseModel):
 
-    sessionToken: str | None = Field(
+    sessionToken: str = Field(
         description = "the session token of the user who is requesting the service",
+        pattern = REGEX_SESSION_TOKEN,
+        default = None,
         frozen = True,
         alias = "X-Session-Token"
     )