calling a class function in another class (invalid use of non-static member function)

I'm creating the first class representing a bank account. The second class represents the registry, using a vector to store objects of the first class. As you can see, I'm calling a function in the main, that calls a function from the second class which calls a function from the first class.

using namespace std;

class Account {
  private:
  string name;
  double balance;
  char allowNegative;

  public:
  Account();
  void setName(string holderName);
  void setAllowNegative(char ynNegative);
  void setBalance(double balance);
  string getName() const;
  double getBalance() const;
  bool yesNegative() const;
};

Account::Account() {
   balance = 0;             
}

class Registry {
  private:
  vector<Account> accounts;

  public:
  bool exists(string holderName);
  void addAcount(Account currAcount);
  Account getAccount(string holderName) const;
};

void Account::setName(string holderName) {
  name = holderName;
}

void Account::setAllowNegative(char ynNegative) {
  allowNegative = ynNegative;
}

void Account::setBalance(double transaction) {
  balance = balance + transaction;
}

string Account::getName() const {
  return name;
}

double Account::getBalance() const {
  return balance;
}

bool Account::yesNegative() const {
  if (allowNegative == 'y') {
    return true;
  }
  return false;
}

bool Registry::exists(string holderName) {
  for (int i = 0; i < accounts.size(); i++) {
    if (accounts.at(i).getName == holderName) {
      return true;
    }
  }
  return false;
}

void Registry::addAcount(Account currAcount) {
  accounts.push_back(currAcount);
}

Account Registry::getAccount(string holderName) const {
  Account tempAccount;
  for (int i = 0; i < accounts.size(); i++) {
    if (accounts.at(i).getName == holderName) {
      tempAccount = accounts.at(i);
      break;
    }
  }
  return tempAccount;
}

And in the main I have this part:

if (!regCopy.exists(holderName)) {
    throw runtime_error("account does not exist");
}

regCopy is an object of class Registry

And I'm getting this error:

I saw many links regarding this problem, most of them include using pointers, and I'm not there yet. So I'm avoiding using that.