diff --git a/pkg/cart/mutation_test.go b/pkg/cart/mutation_test.go
index 0ef7063..302045c 100644
--- a/pkg/cart/mutation_test.go
+++ b/pkg/cart/mutation_test.go
@@ -2,6 +2,8 @@ package cart
 
 import (
 	"context"
+	"encoding/json"
+	"fmt"
 	"reflect"
 	"slices"
 	"strings"
@@ -9,7 +11,6 @@ import (
 	"time"
 
 	"github.com/gogo/protobuf/proto"
-	anypb "google.golang.org/protobuf/types/known/anypb"
 
 	"git.tornberg.me/go-cart-actor/pkg/actor"
 	messages "git.tornberg.me/go-cart-actor/pkg/messages"
@@ -462,12 +463,12 @@ func TestSubscriptionDetailsJSONValidation(t *testing.T) {
 	g := newTestGrain()
 
 	// Valid JSON on create
-	validCreate := &messages.UpsertSubscriptionDetails{
-		OfferingCode: "OFFJSON",
-		SigningType:  "TYPEJSON",
-		Data:         &anypb.Any{Value: []byte(`{"ok":true}`)},
+	jsonStr := `{"offeringCode": "OFFJSON", "signingType": "TYPEJSON", "data": {"value": "eyJvayI6dHJ1ZX0="}}`
+	var validCreate messages.UpsertSubscriptionDetails
+	if err := json.Unmarshal([]byte(jsonStr), &validCreate); err != nil {
+		t.Fatal(err)
 	}
-	applyOK(t, reg, g, validCreate)
+	applyOK(t, reg, g, &validCreate)
 	if len(g.SubscriptionDetails) != 1 {
 		t.Fatalf("expected one subscription detail after valid create, got %d", len(g.SubscriptionDetails))
 	}
@@ -480,41 +481,45 @@ func TestSubscriptionDetailsJSONValidation(t *testing.T) {
 	}
 
 	// Update with valid JSON replaces meta
-	updateValid := &messages.UpsertSubscriptionDetails{
-		Id:   &id,
-		Data: &anypb.Any{Value: []byte(`{"changed":123}`)},
+	jsonStr2 := fmt.Sprintf(`{"id": "%s", "data": {"value": "eyJjaGFuZ2VkIjoxMjN9"}}`, id)
+	var updateValid messages.UpsertSubscriptionDetails
+	if err := json.Unmarshal([]byte(jsonStr2), &updateValid); err != nil {
+		t.Fatal(err)
 	}
-	applyOK(t, reg, g, updateValid)
+	applyOK(t, reg, g, &updateValid)
 	if string(g.SubscriptionDetails[id].Meta) != `{"changed":123}` {
 		t.Fatalf("expected meta updated to new json, got %s", string(g.SubscriptionDetails[id].Meta))
 	}
 
 	// Invalid JSON on create
-	invalidCreate := &messages.UpsertSubscriptionDetails{
-		OfferingCode: "BAD",
-		Data:         &anypb.Any{Value: []byte(`{"broken":}`)},
+	jsonStr3 := `{"offeringCode": "BAD", "signingType": "TYPE", "data": {"value": "eyJicm9rZW4iO30="}}`
+	var invalidCreate messages.UpsertSubscriptionDetails
+	if err := json.Unmarshal([]byte(jsonStr3), &invalidCreate); err != nil {
+		t.Fatal(err)
 	}
-	res := applyOne(t, reg, g, invalidCreate)
+	res := applyOne(t, reg, g, &invalidCreate)
 	if res.Error == nil || !strings.Contains(res.Error.Error(), "invalid json") {
 		t.Fatalf("expected invalid json error on create, got %v", res.Error)
 	}
 
 	// Invalid JSON on update
-	badUpdate := &messages.UpsertSubscriptionDetails{
-		Id:   &id,
-		Data: &anypb.Any{Value: []byte(`{oops`)},
+	jsonStr4 := fmt.Sprintf(`{"id": "%s", "data": {"value": "e29vcHM="}}`, id)
+	var badUpdate messages.UpsertSubscriptionDetails
+	if err := json.Unmarshal([]byte(jsonStr4), &badUpdate); err != nil {
+		t.Fatal(err)
 	}
-	res2 := applyOne(t, reg, g, badUpdate)
+	res2 := applyOne(t, reg, g, &badUpdate)
 	if res2.Error == nil || !strings.Contains(res2.Error.Error(), "invalid json") {
 		t.Fatalf("expected invalid json error on update, got %v", res2.Error)
 	}
 
-	// Empty Data.Value should not overwrite existing meta
-	emptyUpdate := &messages.UpsertSubscriptionDetails{
-		Id:   &id,
-		Data: &anypb.Any{Value: []byte{}},
+	// Empty Data should not overwrite existing meta
+	jsonStr5 := fmt.Sprintf(`{"id": "%s", "data": {"value": ""}}`, id)
+	var emptyUpdate messages.UpsertSubscriptionDetails
+	if err := json.Unmarshal([]byte(jsonStr5), &emptyUpdate); err != nil {
+		t.Fatal(err)
 	}
-	applyOK(t, reg, g, emptyUpdate)
+	applyOK(t, reg, g, &emptyUpdate)
 	if string(g.SubscriptionDetails[id].Meta) != `{"changed":123}` {
 		t.Fatalf("empty update should not change meta, got %s", string(g.SubscriptionDetails[id].Meta))
 	}
diff --git a/pkg/cart/mutation_upsert_subscriptiondetails.go b/pkg/cart/mutation_upsert_subscriptiondetails.go
index 102e547..308f0a7 100644
--- a/pkg/cart/mutation_upsert_subscriptiondetails.go
+++ b/pkg/cart/mutation_upsert_subscriptiondetails.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 
 	messages "git.tornberg.me/go-cart-actor/pkg/messages"
+	"google.golang.org/protobuf/types/known/anypb"
 )
 
 func UpsertSubscriptionDetails(g *CartGrain, m *messages.UpsertSubscriptionDetails) error {
@@ -12,15 +13,33 @@ func UpsertSubscriptionDetails(g *CartGrain, m *messages.UpsertSubscriptionDetai
 		return nil
 	}
 
+	// Helper to get data bytes from Data field
+	getDataBytes := func(data *anypb.Any) ([]byte, error) {
+		if data == nil {
+			return nil, nil
+		}
+		if len(data.Value) > 0 {
+			return data.Value, nil
+		}
+		if data.TypeUrl != "" {
+			return []byte(data.TypeUrl), nil
+		}
+		return nil, nil
+	}
+
 	// Create new subscription details when Id is nil.
 	if m.Id == nil {
 		// Validate JSON if provided.
 		var meta json.RawMessage
-		if m.Data != nil && len(m.Data.Value) > 0 {
-			if !json.Valid(m.Data.Value) {
+		dataBytes, err := getDataBytes(m.Data)
+		if err != nil {
+			return err
+		}
+		if dataBytes != nil {
+			if !json.Valid(dataBytes) {
 				return fmt.Errorf("subscription details invalid json")
 			}
-			meta = json.RawMessage(m.Data.Value)
+			meta = json.RawMessage(dataBytes)
 		}
 
 		id := MustNewCartId().String()
@@ -49,15 +68,16 @@ func UpsertSubscriptionDetails(g *CartGrain, m *messages.UpsertSubscriptionDetai
 		existing.SigningType = m.SigningType
 		changed = true
 	}
-	if m.Data != nil {
-		// Only validate & assign if there is content; empty -> leave as-is.
-		if len(m.Data.Value) > 0 {
-			if !json.Valid(m.Data.Value) {
-				return fmt.Errorf("subscription details invalid json")
-			}
-			existing.Meta = m.Data.Value
-			changed = true
+	dataBytes, err := getDataBytes(m.Data)
+	if err != nil {
+		return err
+	}
+	if dataBytes != nil {
+		if !json.Valid(dataBytes) {
+			return fmt.Errorf("subscription details invalid json")
 		}
+		existing.Meta = dataBytes
+		changed = true
 	}
 	if changed {
 		existing.Version++