diff --git a/cmd/cart/mutation_add_voucher.go b/cmd/cart/mutation_add_voucher.go
index 205438b..53b0952 100644
--- a/cmd/cart/mutation_add_voucher.go
+++ b/cmd/cart/mutation_add_voucher.go
@@ -4,24 +4,37 @@ import (
 	"fmt"
 	"slices"
 
+	"git.tornberg.me/go-cart-actor/pkg/actor"
 	"git.tornberg.me/go-cart-actor/pkg/messages"
 	"git.tornberg.me/go-cart-actor/pkg/voucher"
 )
 
 func (ctx *MutationContext) AddVoucher(g *CartGrain, m *messages.AddVoucher) error {
 	if m == nil {
-		return fmt.Errorf("AddVoucher: nil payload")
+		return &actor.MutationError{
+			Message:    "AddVoucher: nil payload",
+			Code:       1001,
+			StatusCode: 400,
+		}
 	}
 
 	if slices.ContainsFunc(g.Vouchers, func(v *voucher.Voucher) bool {
 		return v.Code == m.Code
 	}) {
-		return fmt.Errorf("voucher already applied")
+		return &actor.MutationError{
+			Message:    "voucher already applied",
+			Code:       1002,
+			StatusCode: 400,
+		}
 	}
 
 	voucherData, err := ctx.VoucherService.GetVoucher(m.Code)
 	if err != nil {
-		return fmt.Errorf("cant find voucher: %w", err)
+		return &actor.MutationError{
+			Message:    fmt.Sprintf("cant find voucher: %v", err),
+			Code:       1003,
+			StatusCode: 400,
+		}
 	}
 
 	if voucherData == nil {
diff --git a/pkg/actor/mutation_registry.go b/pkg/actor/mutation_registry.go
index 1e5f66a..8b3d59d 100644
--- a/pkg/actor/mutation_registry.go
+++ b/pkg/actor/mutation_registry.go
@@ -12,7 +12,7 @@ import (
 type ApplyResult struct {
 	Type     string        `json:"type"`
 	Mutation proto.Message `json:"mutation"`
-	Error    string        `json:"error,omitempty"`
+	Error    error         `json:"error,omitempty"`
 }
 
 type MutationRegistry interface {
@@ -30,9 +30,23 @@ type ProtoMutationRegistry struct {
 }
 
 var (
-	ErrMutationNotRegistered = fmt.Errorf("mutation not registered")
+	ErrMutationNotRegistered = &MutationError{
+		Message:    "mutation not registered",
+		Code:       255,
+		StatusCode: 500,
+	}
 )
 
+type MutationError struct {
+	Message    string `json:"message"`
+	Code       uint32 `json:"code"`
+	StatusCode uint32 `json:"status_code"`
+}
+
+func (m MutationError) Error() string {
+	return m.Message
+}
+
 // MutationOption configures additional behavior for a registered mutation.
 type MutationOption func(*mutationOptions)
 
@@ -167,11 +181,11 @@ func (r *ProtoMutationRegistry) Apply(grain any, msg ...proto.Message) ([]ApplyR
 		entry, ok := r.mutationRegistry[rt]
 		r.mutationRegistryMu.RUnlock()
 		if !ok {
-			results = append(results, ApplyResult{Error: ErrMutationNotRegistered.Error(), Type: rt.Name(), Mutation: m})
+			results = append(results, ApplyResult{Error: ErrMutationNotRegistered, Type: rt.Name(), Mutation: m})
 			continue
 		}
 		err := entry.Handle(grain, m)
-		results = append(results, ApplyResult{Error: err.Error(), Type: rt.Name(), Mutation: m})
+		results = append(results, ApplyResult{Error: err, Type: rt.Name(), Mutation: m})
 	}
 
 	// if entry.updateTotals {