diff --git a/internal/api/handlers/management/auth_files.go b/internal/api/handlers/management/auth_files.go
index e0a16377b..2e471ae8c 100644
--- a/internal/api/handlers/management/auth_files.go
+++ b/internal/api/handlers/management/auth_files.go
@@ -1306,12 +1306,12 @@ func (h *Handler) RequestGeminiCLIToken(c *gin.Context) {
 			projects, errAll := onboardAllGeminiProjects(ctx, gemClient, &ts)
 			if errAll != nil {
 				log.Errorf("Failed to complete Gemini CLI onboarding: %v", errAll)
-				SetOAuthSessionError(state, "Failed to complete Gemini CLI onboarding")
+				SetOAuthSessionError(state, fmt.Sprintf("Failed to complete Gemini CLI onboarding: %v", errAll))
 				return
 			}
 			if errVerify := ensureGeminiProjectsEnabled(ctx, gemClient, projects); errVerify != nil {
 				log.Errorf("Failed to verify Cloud AI API status: %v", errVerify)
-				SetOAuthSessionError(state, "Failed to verify Cloud AI API status")
+				SetOAuthSessionError(state, fmt.Sprintf("Failed to verify Cloud AI API status: %v", errVerify))
 				return
 			}
 			ts.ProjectID = strings.Join(projects, ",")
@@ -1320,7 +1320,7 @@ func (h *Handler) RequestGeminiCLIToken(c *gin.Context) {
 			ts.Auto = false
 			if errSetup := performGeminiCLISetup(ctx, gemClient, &ts, ""); errSetup != nil {
 				log.Errorf("Google One auto-discovery failed: %v", errSetup)
-				SetOAuthSessionError(state, "Google One auto-discovery failed")
+				SetOAuthSessionError(state, fmt.Sprintf("Google One auto-discovery failed: %v", errSetup))
 				return
 			}
 			if strings.TrimSpace(ts.ProjectID) == "" {
@@ -1331,19 +1331,19 @@ func (h *Handler) RequestGeminiCLIToken(c *gin.Context) {
 			isChecked, errCheck := checkCloudAPIIsEnabled(ctx, gemClient, ts.ProjectID)
 			if errCheck != nil {
 				log.Errorf("Failed to verify Cloud AI API status: %v", errCheck)
-				SetOAuthSessionError(state, "Failed to verify Cloud AI API status")
+				SetOAuthSessionError(state, fmt.Sprintf("Failed to verify Cloud AI API status: %v", errCheck))
 				return
 			}
 			ts.Checked = isChecked
 			if !isChecked {
 				log.Error("Cloud AI API is not enabled for the auto-discovered project")
-				SetOAuthSessionError(state, "Cloud AI API not enabled")
+				SetOAuthSessionError(state, fmt.Sprintf("Cloud AI API not enabled for project %s", ts.ProjectID))
 				return
 			}
 		} else {
 			if errEnsure := ensureGeminiProjectAndOnboard(ctx, gemClient, &ts, requestedProjectID); errEnsure != nil {
 				log.Errorf("Failed to complete Gemini CLI onboarding: %v", errEnsure)
-				SetOAuthSessionError(state, "Failed to complete Gemini CLI onboarding")
+				SetOAuthSessionError(state, fmt.Sprintf("Failed to complete Gemini CLI onboarding: %v", errEnsure))
 				return
 			}
 
@@ -1356,13 +1356,13 @@ func (h *Handler) RequestGeminiCLIToken(c *gin.Context) {
 			isChecked, errCheck := checkCloudAPIIsEnabled(ctx, gemClient, ts.ProjectID)
 			if errCheck != nil {
 				log.Errorf("Failed to verify Cloud AI API status: %v", errCheck)
-				SetOAuthSessionError(state, "Failed to verify Cloud AI API status")
+				SetOAuthSessionError(state, fmt.Sprintf("Failed to verify Cloud AI API status: %v", errCheck))
 				return
 			}
 			ts.Checked = isChecked
 			if !isChecked {
 				log.Error("Cloud AI API is not enabled for the selected project")
-				SetOAuthSessionError(state, "Cloud AI API not enabled")
+				SetOAuthSessionError(state, fmt.Sprintf("Cloud AI API not enabled for project %s", ts.ProjectID))
 				return
 			}
 		}