## ❌ Upvoting PYQ Fails – `branch` field casting error

### 🐛 Description:
When trying to upvote a PYQ, a `400 Bad Request` error is returned from the backend. The response suggests a validation failure related to the `branch` field.

---

### 💥 Error (from network tab):

```json
{
"error": "Failed to upvote PYQ",
"details": "pyqs validation failed: branch: Cast to ObjectId failed for value \"CSE\" (type string) at path \"branch\" because of \"BSONError\""
}