Review and optimization of user API implementation

It is necessary to analyze the provided API code fragment responsible for user management, identify potential issues, and suggest improvements in the implementation.

func isValidName(name string) error {
  if len(name) > 50 {
    return errors.New("invalid name length")
  }
  return nil
}

func isValidPhone(phone string) error {
  if len(phone) != 11 {
    return errors.New("invalid phone format")
  }
  return nil
}

type User struct {
  Id         int       `json:"id"`
  Name       string    `json:"name"`
  Phone      string    `json:"phone"`
  IsAdmin    bool      `json:"is_admin"`
  CreatedAt  time.Time `json:"created_at"`
  UpdatedAt  time.Time `json:"updated_at"`
}

type UserRepository interface {
  Find(sql string) *User
  Save(user *User) *User
}

type UserApi struct {
  userRepo UserRepository
  logger   *zap.Logger
}

func NewUserApi(userRepo UserRepository) *UserApi {
  api := &UserApi{
    userRepo: userRepo,
  }

  if os.Getenv("ENV") == "prod" {
    api.logger, _ = zap.NewProduction()
  } else {
    api.logger, _ = zap.NewDevelopment()
  }

  return api
}

func (api *UserApi) ProcessRequest(c *gin.Context) {
  authUserId := c.GetInt("auth_user_id")
  authUser := api.userRepo.Find(fmt.Sprintf("SELECT * FROM user WHERE id = %d", authUserId))

  id := c.Query("id")
  user := api.userRepo.Find(fmt.Sprintf("SELECT * FROM user WHERE id = %s", id))

  if authUser.IsAdmin || authUser.Id == user.Id {
    if c.Request.Method == "POST" {
      bytes, _ := io.ReadAll(c.Request.Body)
      var body map[string]string
      json.Unmarshal(bytes, &body)

      var errs map[string]string

      if err := isValidName(body["name"]); err != nil {
        errs["name"] = err.Error()
      } else {
        user.Name = body["name"]
      }

      if err := isValidPhone(body["phone"]); err != nil {
        errs["phone"] = err.Error()
      } else {
        user.Phone = body["phone"]
      }

      if len(errs) > 0 {
        c.JSON(http.StatusUnprocessableEntity, errs)
        return
      }

      user.UpdatedAt = time.Now()

      api.userRepo.Save(user)
      api.logger.Debug("user saved", zap.Int("user_id", user.Id))
      c.JSON(http.StatusOK, user)
      return
    }
  }

  c.Status(http.StatusForbidden)
}

func main() {
    // It's implemented somehow
    api := NewUserApi(...)
    r := gin.Default()
    r.POST("/users", api.ProcessRequest)
    r.Run()
}