Shortcode attributes not working on wordpress

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PHP

API

WordPress

I am experiencing an issue where the 'to' and 'from' attributes in my shortcode are working properly, but the 'amount' parameter is not. When attempting to change the value of the 'amount' parameter through the shortcode, the result is of always 1.

using the shortcode like this:
[exchange_rate from="USD" to="EUR" amount="100"]

What I have tried:

function currency_conversion_shortcode($atts) {
    $atts = shortcode_atts( array(
        'amount' => '1',
        'from' => 'USD',
        'to' => 'EUR',
    ), $atts, 'currency_conversion' );

    if (!is_numeric($atts['amount'])) {
        return "Invalid amount passed. Please pass a valid numeric value.";
    }

    $api_key = 'xxxxx-xxxx-xxxx';
    $url = "https://api.fastforex.io/convert?from=" . $atts['from'] . "&to=" . $atts['to'] . "&amount=" . $atts['amount'] . "&api_key=" . $api_key;

    $result = file_get_contents($url);
    if ($result === false) {
        return "Error: Failed to fetch data from API.";
    }

    $result = json_decode($result, true);
    if (!isset($result['result']['rate'])) {
        return "Error: Invalid response from API.";
    }

    return $atts['amount'] . " " . $atts['from'] . " = " . $result['result']['rate'] . " " . $atts['to'];
}

add_shortcode('currency_conversion', 'currency_conversion_shortcode');