Can't add relationship attribute

Hi
I'm running a script that adds a relationship between two CIs. It work but it dosen't enter the value for the relationship attribute.

There is a attribute for the relationship which I can add manually.

I can't add the relationship with the attribute from the API documentation either.

XML:
<API version='1.0' locale='en'>
<records>
<relationships>
<addrelationship>
<toci>System Z</toci>
<relationshiptype>Managed by</relationshiptype>
<relatedcis>
<citype>Technician</citype>
<ci>
<name>Some One</name>
<relationattributes>
<attribute>
<name>Level</name>
<value>1</value>
</attribute>
</relationattributes>
</ci>
</relatedcis>
</addrelationship>
</relationships>
</records>
</API>

Is there something I'm doing wrong?

We are running version 9.3, 9326