Create application/atom+xml result

Question

I have an API on GoogleCloud and need to define an endpoint which returns a feed usable in Excel PowerPivot and Power BI. I have found this library using feed.ToAtom(), but the created feed does not work in PoverPivot, I get the following error: The payload kind 'Value' of the given data feed is not supported. but I can't find any information.

How can I create the needed result?

Here a snipped of the current result:

<?xml version="1.0" encoding="UTF-8"?>
<feed
    xmlns="http://www.w3.org/2005/Atom">
    <title>dfhfdhsfdh.net blog</title>
    <id>http://dfhfdhsfdh.net/blojhlkjluizg</id>
    <updated>2022-05-19T07:51:07+02:00</updated>
    <rights>sdfsdf</rights>
    <subtitle>discussion about tech, footie, photos</subtitle>
    <link href="http://dfhfdhsfdh.net/blojhlkjluizg"></link>
    <author>
        <name>ergsrdg sdfgsfdg</name>
        <email>dfhfdhsfdh@dfhfdhsfdh.net</email>
    </author>
    <entry>
        <title>22906201</title>
        <updated>2022-05-19T07:51:07+02:00</updated>
        <id>http://dfhfdhsfdh.net/sdfsdfblog</id>
        <link href="http://dfhfdhsfdh.net/blfghjghjog" rel="alternate"></link>
        <summary type="html"></summary>
    </entry>
    <entry>
        <title>22906197</title>
        <updated>2022-05-19T07:51:07+02:00</updated>
        <id>http://dfhfdhsfdh.net/sdfsdfblog</id>
        <link href="http://dfhfdhsfdh.net/blfghjghjog" rel="alternate"></link>
        <summary type="html"></summary>
    </entry>
</feed>

I have also created the result by my self, the result is the following, but still get that error:

<?xml version="1.0" encoding="UTF-8"?>
<feed
    xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices"
    xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"
    xmlns="http://www.w3.org/2005/Atom">
    <title type="text">Guest Requests</title>
    <id>http://localhost:4444/requests/GuestRequests/</id>
    <updated>2022-05-19T09:33:40+02:00</updated>
    <entry>
        <id>http://localhost:4444/requests/22906201</id>
        <title type="text">22906201</title>
        <updated>2022-05-19T09:33:40+02:00</updated>
        <author>
            <name>TODO</name>
        </author>
        <content type="application/xml">
            <m:properties>
                <d:id>22906201</d:id>
                <d:title>22906201</d:title>
            </m:properties>
        </content>
    </entry>
</feed>