fix(pc): use correct error

Author: GAlexIHU

e2e/productcatalog_test.go

@@ -360,14 +360,15 @@ func TestPlan(t *testing.T) {
 		misalignedCreate.Alignment = &api.Alignment{
 			BillablesMustAlign: lo.ToPtr(true),
 		}
+		misalignedCreate.BillingCadence = "P1M"
 
 		misalignedCreate.Phases = slices.Clone(planCreate.Phases)
 		misalignedCreate.Phases[0].RateCards = slices.Clone(planCreate.Phases[0].RateCards)
 		misalignedCreate.Phases[0].RateCards = []api.RateCard{maP1RC1, maP1RC2}
 
 		planAPIRes, err := client.CreatePlanWithResponse(ctx, misalignedCreate)
 		require.Nil(t, err)
-		require.Equal(t, 201, planAPIRes.StatusCode())
+		require.Equal(t, 201, planAPIRes.StatusCode(), "received the following body: %s", planAPIRes.Body)
 
 		plan := planAPIRes.JSON201
 		require.NotNil(t, plan, "received the following body: %s", planAPIRes.Body)

openmeter/productcatalog/alignment.go

@@ -1,8 +1,6 @@
 package productcatalog
 
 import (
-	"fmt"
-
 	"github.com/openmeterio/openmeter/pkg/isodate"
 )
 
@@ -43,5 +41,5 @@ func ValidateBillingCadencesAlign(planBillingCadence isodate.Period, rateCardBil
 		return nil
 	}
 
-	return fmt.Errorf("billing cadences do not align: %s and %s", planBillingCadence, rateCardBillingCadence)
+	return ErrRateCardBillingCadenceUnaligned
 }