Some additional info needed

Just to continue previous topic with your another (rate) plugin can we use the same code to transfer converted data to checkout ? I mean this code

nope, this is another.

The thing is that the plugin is designed in such a way that the conversion process happens instantly as soon as a person has entered the required amount and the button there is of no use. But if you want to click on the button separately to send a request – it is possible. The main thing is that users should realize that they need to do one more additional action, because as I wrote earlier – the conversion process happens instantly when the value is entered.

document.addEventListener('DOMContentLoaded', function () {
    // Function to initialize the event listener once the converter is rendered
    function initializeSendButton() {
        const inputField = document.querySelector('.cr-exchange-rates .amount input');
        const sendButton = document.querySelector('.send-button'); // YOUR CUSTOM BUTTON!!!
        const resultField = document.querySelector('.cr-exchange-rates .result');

        if (!inputField || !sendButton || !resultField) return; // If any required elements are not available, exit

        // Add a click event listener to the "Send" button
        sendButton.addEventListener('click', function () {
            const amount = inputField.value; // Get the amount entered by the user
            const result = resultField.textContent; // Get the result of the conversion

            // Send the collected data to the server
            fetch('/path-to-your-server-endpoint', {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json',
                },
                body: JSON.stringify({
                    amount: amount,
                    fromCurrency: document.querySelector('.cr-exchange-rates select').value, // Get the selected "from" currency
                    toCurrency: document.querySelector('.cr-exchange-rates select:last-child').value, // Get the selected "to" currency
                    conversionResult: result // Include the conversion result in the data sent to the server
                }),
            })
            .then(response => response.json())
            .then(data => {
                console.log('Conversion logged:', data); // Log the response data for debugging
            })
            .catch(error => {
                console.error('Error:', error); // Log any errors that occur
            });
        });
    }

    // Use a MutationObserver to detect when the converter is added to the DOM
    const observer = new MutationObserver((mutationsList) => {
        for (let mutation of mutationsList) {
            if (mutation.type === 'childList') {
                if (document.querySelector('.cr-exchange-rates')) {
                    // If the currency converter is found, initialize the send button listener
                    initializeSendButton();
                    observer.disconnect(); // Stop observing once initialized
                }
            }
        }
    });

    // Start observing the body for added nodes (i.e., when the converter is injected into the DOM)
    observer.observe(document.body, { childList: true, subtree: true });
});

What you write is not a trivial case for this widget. This needs to be seen on your website.