diff --git a/go-backend/internal/services/altcha_service.go b/go-backend/internal/services/altcha_service.go
index e9f3670..260025e 100644
--- a/go-backend/internal/services/altcha_service.go
+++ b/go-backend/internal/services/altcha_service.go
@@ -50,7 +50,7 @@ func (s *AltchaService) VerifyToken(token, remoteIP string) (*AltchaResponse, er
 func (s *AltchaService) GenerateChallenge() (map[string]interface{}, error) {
 	// Generate challenge using official ALTCHA library
 	options := altcha.ChallengeOptions{
-		Algorithm:  altcha.AlgorithmSHA256,
+		Algorithm:  "SHA-256",
 		MaxNumber:  100000,
 		SaltLength: 12,
 		HMACKey:    s.secretKey,