btcpayserver/BTCPayServer/Plugins/Subscriptions/Views/UIOffering/ChangeCreditModal.cshtml

<div class="modal fade" id="updateCreditModal" tabindex="-1" aria-hidden="true">
    <div class="modal-dialog modal-dialog-centered">
        <div class="modal-content">
            <div class="modal-header">
                <h4 class="modal-title charge-mode" text-translate="true">Charge user</h4>
                <h4 class="modal-title credit-mode" text-translate="true">Credit user</h4>
                <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="@StringLocalizer["Close"]">
                    <vc:icon symbol="close" />
                </button>
            </div>
            <form method="post">
                <div class="modal-body">
                    <div html-translate="true" class="charge-mode">Would you like to charge <span class="subscriber-name fw-semibold"></span>?</div>
                    <div html-translate="true" class="credit-mode">Would you like to credit <span class="subscriber-name fw-semibold"></span>?</div>
                </div>
                <div class="modal-body pt-0 pb-0">
                    <input name="customerId" type="hidden" />

                    <div class="d-flex justify-content-between credit-plan-price">
                        <div class="text-muted">Current credit</div>
                        <div class="current-credit"></div>
                    </div>
                    <div class="d-flex justify-content-between align-items-center charge-applied">
                        <div class="text-muted charge-mode">Charge applied</div>
                        <div class="text-muted credit-mode">Credit applied</div>
                        <div class="d-flex align-items-center justify-content-end">
                            <span class="charge-mode">-</span>
                            <span class="credit-mode">+</span>
                            <input type="text"
                                   class="form-control form-control-sm amount ms-2"
                                   name="amount"
                                   style="text-align: right;"
                                   autocomplete="off" />
                        </div>
                    </div>
                    <hr />
                    <div class="d-flex justify-content-between fw-semibold credit-next-charge">
                        <div class="charge-mode">After charge</div>
                        <div class="credit-mode">After Credit</div>
                        <div class="after-change"></div>
                    </div>
                </div>
                <div class="modal-footer">
                    <button type="submit" class="btn btn-danger charge-mode" text-translate="true" name="command" value="charge">Charge</button>
                    <button type="submit" class="btn btn-success credit-mode" text-translate="true" name="command" value="credit">Credit</button>
                </div>
            </form>
        </div>
    </div>
</div>

<script>
    document.addEventListener('DOMContentLoaded', function () {
        (function () {
            const modalChargeEl = document.getElementById('updateCreditModal');
            const idEl = modalChargeEl.querySelector('input[name="customerId"]');
            const currentCredit = modalChargeEl.querySelector('.current-credit');
            const afterChangeEl = modalChargeEl.querySelector('.after-change');
            const amount = modalChargeEl.querySelector('.amount');
            var creditMode = false;

            var seq = 0;
            var currency;
            var currentCreditValue = 0;
            amount.addEventListener('input', updateChargeAfter);

            async function getFormattedValue(value, currency) {
                const response = await fetch(`format-currency`, {
                    method: 'POST',
                    headers: {
                        'Content-Type': 'application/json'
                    },
                    body: JSON.stringify({
                        amount: value,
                        currency: currency
                    })
                });
                return await response.text();
            }

            let debounceTimeout;

            async function updateChargeAfter() {
                const amountValue = Number(amount.value) || 0;
                modalChargeEl.querySelectorAll('button[name="command"]').forEach(el => el.disabled = amountValue <= 0);

                const remaining = creditMode ? currentCreditValue + amountValue : currentCreditValue - amountValue;

                // Debounce the updates to avoid flooding the service
                const DEBOUNCE_DELAY = 300; // 300ms delay

                // Create a debounced update function
                const debouncedUpdate = async () => {
                    seq++;
                    var thisSeq = seq;
                    afterChangeEl.innerText = '---';
                    if (thisSeq !== seq) return;
                    afterChangeEl.innerText = await getFormattedValue(remaining, currency);
                };

                if (debounceTimeout) clearTimeout(debounceTimeout);
                afterChangeEl.innerText = '...';
                debounceTimeout = setTimeout(debouncedUpdate, DEBOUNCE_DELAY);
            }

            modalChargeEl.addEventListener('show.bs.modal', function (event) {
                const trigger = event.relatedTarget;
                if (!trigger) return;

                const tr = trigger.closest('tr');
                currency = tr.getAttribute('data-currency');
                currentCreditValue = Number(tr.getAttribute('data-current-credit-value'));
                if (idEl) idEl.value = tr.getAttribute('data-subscriber-id');

                modalChargeEl.querySelectorAll('.subscriber-name').forEach(el => el.innerText = tr.getAttribute('data-subscriber-email'));

                creditMode = trigger.getAttribute('data-action') === 'credit';
                const chargeModeEls = modalChargeEl.querySelectorAll('.charge-mode');
                const creditModeEls = modalChargeEl.querySelectorAll('.credit-mode');
                if (creditMode) {
                    chargeModeEls.forEach(el => el.style.display = 'none');
                    creditModeEls.forEach(el => el.style.display = '');
                    modalChargeEl.querySelectorAll('button[name="command"]').forEach(el => el.value = 'credit');
                } else {
                    chargeModeEls.forEach(el => el.style.display = '');
                    creditModeEls.forEach(el => el.style.display = 'none');
                    modalChargeEl.querySelectorAll('button[name="command"]').forEach(el => el.value = 'charge');
                }

                currentCredit.innerText = '---';
                getFormattedValue(currentCreditValue, currency).then(value => currentCredit.innerText = value);
                amount.value = '';
                afterChangeEl.innerText = '';
                updateChargeAfter();
            });
        })();
    });
</script>