Maybe this is the reason. our host is located in XXXXXXX.execute-api.cn-northwest-1.amazonaws.com.cn. But the host which is generated by Get SigV4 Headers is XXXXXXX.execute-api.cn-northwest-1.amazonaws.com.
I also update this host in Rest Call, but this is useless. Because the Authorization is generated with amazonaws.com, not amazonawsaws.com.cn.