1. Go to Setup | Sites | Charket site,
(1) Set Clickjack Protection Level to Allow framing of site or community pages on external domains (Good protection).
(2) Add your website domain to Whitelisted Domains for Inline Frames.
2. Add the parameter isdtp=vw to the Form URL, likes below:
<apex:iframe src="https://staging4.dev.customer.charket.com.cn/charket__form?id=a050b000021PAYCAA4&isdtp=vw"/>