Fix client API return type for send invite error

clientapi/routing/membership.go

@@ -223,7 +223,10 @@ func SendInvite(
 	)
 	if err != nil {
 		util.GetLogger(req.Context()).WithError(err).Error("roomserverAPI.SendInvite failed")
-		return jsonerror.InternalServerError()
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.Forbidden(err.Error()),
+		}
 	}
 	return util.JSONResponse{
 		Code: http.StatusOK,

roomserver/api/wrapper.go

@@ -125,7 +125,7 @@ func SendInvite(
 				Kind:         KindNew,
 				Event:        inviteEvent,
 				AuthEventIDs: inviteEvent.AuthEventIDs(),
-				SendAsServer: DoNotSendToOtherServers,
+				SendAsServer: string(sendAsServer),
 			},
 		},
 	}

roomserver/internal/perform_invite.go

@@ -2,6 +2,7 @@ package internal
 
 import (
 	"context"
+	"errors"
 	"fmt"
 
 	federationSenderAPI "github.com/matrix-org/dendrite/federationsender/api"
@@ -95,10 +96,7 @@ func (r *RoomserverInternalAPI) PerformInvite(
 		// For now we will implement option 2. Since in the abesence of a retry
 		// mechanism it will be equivalent to option 1, and we don't have a
 		// signalling mechanism to implement option 3.
-		return &api.PerformError{
+		return errors.New("The user is already in the room")
-			Code: api.PerformErrorNoOperation,
-			Msg:  "user is already joined to room",
-		}
 	}
 
 	if isOriginLocal {