This feed does not validate.
<feed xml:lang="en" xmlns="http://www.w3.org/2005/Atom" xmlns:opensearch="ht ...
In addition, interoperability with the widest range of feed readers could be improved by implementing the following recommendation.
<feed xml:lang="en" xmlns="http://www.w3.org/2005/Atom" xmlns:opensearch="ht ...
<?xml version="1.0" encoding="UTF-8"?>
<feed xml:lang="en" xmlns="http://www.w3.org/2005/Atom" xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/" xmlns:s="http://jadedpixel.com/-/spec/shopify">
<id>https://www.bangbang.com.hk/collections/all.atom</id>
<link rel="alternate" type="text/html" href="https://www.bangbang.com.hk/collections/all"/>
<link rel="self" type="application/atom+xml" href="https://www.bangbang.com.hk/collections/hammer-hammer-housing-sears.atom"/>
<title>Bang Bang Airsoft</title>
<author>
<name>Bang Bang Airsoft</name>
</author>
</feed>