REST API POST field relation error must be defined

Questions and Answers Strapi Backend
2

i solved the problem by create custom controller and using core action with query

  const user = await strapi.db
        .query("plugin::users-permissions.user")
        .findOne({
          where: { id: userId },
        });

      if (!user) {
        throw new ValidationError("userId title must be defined.");
      }

      const result = await super.create(ctx);

      if (!!result && result?.data) {
        await strapi.db.query("api::leave-detail.leave-detail").update({
          where: { id: result.data.id },
          data: { user: userId },
        });
      }