Display Errors
If there is a payment error, your page will reload with a variable that uses the same name as your payment form handle. If you form handle is paymentForm your errors will be available to you via paymentForm.getErrors().
{% if paymentForm is defined and paymentForm.getErrors() | length %}
{% for errors in paymentForm.getErrors() %}
<ul class="errors">
{% for error in errors %}
<li>{{ error }}</li>
{% endfor %}
</ul>
{% endfor %}
{% endif %}