diff --git a/internal/app/participation.go b/internal/app/participation.go
index 4ce150f..0f83314 100644
--- a/internal/app/participation.go
+++ b/internal/app/participation.go
@@ -31,6 +31,9 @@ func participationError(err error) string {
 }
 func (s *server) GetParticipation(ctx context.Context, req *proto.GetParticipationReq) (*proto.ParticipationRsp, error) {
 	_ = grpc.SetHeader(ctx, metadata.Pairs("Cache-Control", "no-store"))
+	if req == nil {
+		return &proto.ParticipationRsp{Error: participationError(participation_service.ErrParticipationLink)}, nil
+	}
 	p, err := s.participationService.GetParticipation(ctx, req.Token)
 	result := mapParticipationResponse(p)
 	if err != nil {
@@ -40,8 +43,11 @@ func (s *server) GetParticipation(ctx context.Context, req *proto.GetParticipati
 }
 func (s *server) AnswerParticipation(ctx context.Context, req *proto.AnswerParticipationReq) (*proto.ParticipationRsp, error) {
 	_ = grpc.SetHeader(ctx, metadata.Pairs("Cache-Control", "no-store"))
+	if req == nil {
+		return &proto.ParticipationRsp{Error: participationError(participation_service.ErrParticipationLink)}, nil
+	}
 	if req.Answer != "confirmed" && req.Answer != "cancelled" {
-		return &proto.ParticipationRsp{Error: "Выберите подтверждение или отмену участия"}, nil
+		return &proto.ParticipationRsp{Error: participation_service.ErrInvalidAnswer.Error()}, nil
 	}
 	p, err := s.participationService.AnswerParticipation(ctx, req.Token, req.Answer)
 	result := mapParticipationResponse(p)
diff --git a/internal/app/participation_test.go b/internal/app/participation_test.go
new file mode 100644
index 0000000..3b7e1ea
--- /dev/null
+++ b/internal/app/participation_test.go
@@ -0,0 +1,31 @@
+package app
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	"evening_detective_server/internal/services/participation_service"
+)
+
+func TestParticipationError(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"invalid link", participation_service.ErrParticipationLink, "Ссылка недействительна"},
+		{"closed", participation_service.ErrParticipationClosed, "Приём ответов закрыт"},
+		{"final", participation_service.ErrParticipationFinal, "Решение уже принято и не может быть изменено"},
+		{"internal", errors.New("private database detail"), "Не удалось обработать ответ. Попробуйте позже."},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := participationError(tc.err); got != tc.want {
+				t.Fatalf("message=%q, want %q", got, tc.want)
+			}
+			if strings.Contains(participationError(tc.err), "private database detail") {
+				t.Fatal("private error exposed")
+			}
+		})
+	}
+}
diff --git a/internal/services/participation_service/participation.go b/internal/services/participation_service/participation.go
index 42886e5..0cf9755 100644
--- a/internal/services/participation_service/participation.go
+++ b/internal/services/participation_service/participation.go
@@ -1,9 +1,8 @@
 package participation_service
 
 import (
+	"errors"
 	"time"
-
-	"evening_detective_server/internal/repos/teams_repo"
 )
 
 // Participation — данные участия, доступные транспортному и email-сценариям.
@@ -20,7 +19,8 @@ type Participation struct {
 }
 
 var (
-	ErrParticipationLink   = teams_repo.ErrParticipationLink
-	ErrParticipationClosed = teams_repo.ErrParticipationClosed
-	ErrParticipationFinal  = teams_repo.ErrParticipationFinal
+	ErrParticipationLink   = errors.New("Ссылка недействительна")
+	ErrParticipationClosed = errors.New("Приём ответов закрыт")
+	ErrParticipationFinal  = errors.New("Решение уже принято и не может быть изменено")
+	ErrInvalidAnswer       = errors.New("Выберите подтверждение или отмену участия")
 )
diff --git a/internal/services/participation_service/service.go b/internal/services/participation_service/service.go
index 099fdf4..2a023a1 100644
--- a/internal/services/participation_service/service.go
+++ b/internal/services/participation_service/service.go
@@ -30,11 +30,26 @@ func NewParticipationService(teamsRepo *teams_repo.TeamsRepo, appBaseURL string)
 
 func (s *ParticipationService) GetParticipation(ctx context.Context, token string) (*Participation, error) {
 	p, err := s.teamsRepo.GetParticipation(ctx, token)
-	return mapParticipation(p), err
+	return mapParticipation(p), mapParticipationError(err)
 }
 func (s *ParticipationService) AnswerParticipation(ctx context.Context, token, answer string) (*Participation, error) {
 	p, err := s.teamsRepo.AnswerParticipation(ctx, token, answer)
-	return mapParticipation(p), err
+	return mapParticipation(p), mapParticipationError(err)
+}
+
+func mapParticipationError(err error) error {
+	switch {
+	case errors.Is(err, teams_repo.ErrParticipationLink):
+		return ErrParticipationLink
+	case errors.Is(err, teams_repo.ErrParticipationClosed):
+		return ErrParticipationClosed
+	case errors.Is(err, teams_repo.ErrParticipationFinal):
+		return ErrParticipationFinal
+	case err != nil && err.Error() == ErrInvalidAnswer.Error():
+		return ErrInvalidAnswer
+	default:
+		return err
+	}
 }
 
 // Стабильные токены для разных целей сохраняют работоспособность ссылок при