ProGet Maven Repository Feed API Access

I am attempting to publish maven builds to a ProGet feed using an API key from a Jenkins server. However, I continue to get an Unauthorized response from the ProGet server. I have my repository setup in my settings.xml file as such:

            <repository>
                <id>snapshots</id>
                <name>ProGet Snapshots</name>
                <releases>
                    <enabled>false</enabled>
                    <updatePolicy>always</updatePolicy>
                    <checksumPolicy>warn</checksumPolicy>
                </releases>
                <snapshots>
                    <enabled>true</enabled>
                    <updatePolicy>never</updatePolicy>
                    <checksumPolicy>fail</checksumPolicy>
                </snapshots>
                <url>https://proget.domain.com/maven2/snapshots?key=00000000000</url>
                <layout>default</layout>
            </repository>

Is there something wrong with my maven settings, or an authentication problem on ProGet?

Many thanks.