Date change function in PHP

I was using this to get date string with $caquantidadeparcelas (define number of dates), and $caprimeirovencimento (first date to reference), but cannot find why is not working as expected, can someone explain?

<?php
    function gerarDatasPagamento($dataInicialStr, $caquantidadeparcelas) {
        // Converte a string da data inicial para um objeto DateTime
        $caprimeirovencimento = new DateTime($dataInicialStr);
                    
        // Array para armazenar as datas de pagamento
        $datasPagamento = [];
                    
        // Adiciona a data inicial ao array
        $datasPagamento[] = $caprimeirovencimento->format('d-m-Y');
                    
        // Gera as datas subsequentes com um mês de diferença
        for ($i = 1; $i < $caquantidadeparcelas; $i++) {
            $caprimeirovencimento->modify('+1 month');
            $datasPagamento[] = $caprimeirovencimento->format('d-m-Y');
        }
                    
        return $datasPagamento;
    }

    $due_dates = gerarDatasPagamento($caprimeirovencimento, $caquantidadeparcelas);

    foreach ($due_dates as $index => $date) {
        echo ($index + 1) . "° vencimento: " . $date . "&nbsp;";
    } ?>

i tried to change function but the problem is in date format sometimes recognizes month as day, and eventually generates fatal error

It looks like you’re trying to handle an invalid date input in PHP. Below is the code you can consider:

function generatePaymentDates($initialDateStr, $numberOfInstallments) {
    $format = 'd-m-Y';
    $firstDueDate = DateTime::createFromFormat($format, $initialDateStr);

    if (!$firstDueDate) {
        return "Invalid date provided. Make sure it is in the $format format.";
    }

    $paymentDates = [];
    $paymentDates[] = $firstDueDate->format($format);

    for ($i = 1; $i < $numberOfInstallments; $i++) {
        $firstDueDate->modify('+1 month');
        $paymentDates[] = $firstDueDate->format($format);
    }

    return $paymentDates;
}

$result = generatePaymentDates($firstDueDate, $numberOfInstallments);

if (is_array($result)) {
    foreach ($result as $index => $date) {
        echo ($index + 1) . "° due date: " . $date . "&nbsp;";
    }
} else {
    echo $result; // Display error message
}