diff --git a/handlers.go b/handlers.go
index 690d8e9..1615d0e 100644
--- a/handlers.go
+++ b/handlers.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"os"
 )
 
 // RegistrationRequest represents the incoming registration request.
@@ -13,16 +14,22 @@ type RegistrationRequest struct {
 }
 
 func registerHandler(w http.ResponseWriter, r *http.Request) {
-	// Allow only POST method
+	// Allow only POST requests
 	if r.Method != http.MethodPost {
 		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
 		return
 	}
 
-	// Parse the request body into the RegistrationRequest struct
+	// Parse the request body
 	var req RegistrationRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		http.Error(w, "Invalid request body", http.StatusBadRequest)
+		http.Error(w, fmt.Sprintf("Invalid request body: %v", err), http.StatusBadRequest)
+		return
+	}
+
+	// Validate email
+	if !validateEmailDomain(req.Email) {
+		http.Error(w, "Email domain is not allowed", http.StatusBadRequest)
 		return
 	}
 
@@ -38,11 +45,21 @@ func registerHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Initialize Overleaf instance
-	overleaf := NewOverleaf("http://localhost:3000") // Replace with the actual Overleaf base URL
+	baseURL := os.Getenv("OL_INSTANCE")
+	if baseURL == "" {
+		http.Error(w, "OL_INSTANCE is not set", http.StatusInternalServerError)
+		return
+	}
+	overleaf := NewOverleaf(baseURL)
+
+	// Admin login using environment variables
+	adminEmail := os.Getenv("OL_ADMIN_EMAIL")
+	adminPassword := os.Getenv("OL_ADMIN_PASSWORD")
+	if adminEmail == "" || adminPassword == "" {
+		http.Error(w, "OL_ADMIN_EMAIL or OL_ADMIN_PASSWORD is not set", http.StatusInternalServerError)
+		return
+	}
 
-	// Optional: Log in as admin (if needed for user creation)
-	adminEmail := "admin@example.com" // Replace with actual admin email
-	adminPassword := "adminpassword"  // Replace with actual admin password
 	if err := overleaf.Login(adminEmail, adminPassword); err != nil {
 		http.Error(w, fmt.Sprintf("Admin login failed: %v", err), http.StatusInternalServerError)
 		return
@@ -55,6 +72,9 @@ func registerHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Respond with success
+	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusOK)
-	w.Write([]byte("User registered successfully. Please check your email to set your password."))
+	json.NewEncoder(w).Encode(map[string]string{
+		"message": "User registered successfully. Please check your email to set your password.",
+	})
 }