<script src="https://securepay.tinkoff.ru/html/payForm/js/tinkoff_v2.js"></script>
<form name="TinkoffPayForm" onsubmit="pay(this); return false;">
	<input class="tinkoffPayRow" type="hidden" name="terminalkey" value="TinkoffBankTest">
	<input class="tinkoffPayRow" type="hidden" name="frame" value="true">
	<input class="tinkoffPayRow" type="hidden" name="language" value="ru">
    <input class="tinkoffPayRow" type="text" placeholder="Сумма заказа" name="amount" required>
    <input class="tinkoffPayRow" type="text" placeholder="Номер заказа" name="order">
    <input class="tinkoffPayRow" type="text" placeholder="Описание заказа" name="description">
    <input class="tinkoffPayRow" type="text" placeholder="ФИО плательщика" name="name">
    <input class="tinkoffPayRow" type="text" placeholder="E-mail" name="email">
    <input class="tinkoffPayRow" type="text" placeholder="Контактный телефон" name="phone">
    <input class="tinkoffPayRow" type="submit" value="Оплатить">
</form>

//Попробуйте так
const Form=document.querySelector('[name="TinkoffPayForm"]');
Form.dispatchEvent(new Event('submit'));
//или так
Form.querySelector('[type="submit"]').dispatchEvent(new Event('click'));

document.querySelector('form[name="TinkoffPayForm"] [type="submit"]').click();