Cannot SetValue on Multi-value attribute. Use AddValue and RemoveValue while create an Epic Asset using Version One API

I am getting error in the creation of an asset of type 'Epic' using version one API. Here is my request URL:

URL:<Domain>/rest-1.v1/Data/Epic

Request body:

<?xml version="1.0" encoding="UTF-8"?>
<Asset href="<Domain>/rest-1.v1/New/Epic">
    <Attribute name="Name" act="set">Test Epic Creation</Attribute>
    <Relation name="Category">
        <Asset href="<Domain>/rest-1.v1/Data/EpicCategory/207" idref="EpicCategory:207"/>
    </Relation>
    <Attribute name="Category" act="set">EpicCategory:207</Attribute>
    <Attribute name="Status" act="set">EpicStatus:64</Attribute>
    <Attribute name="Custom_Product" act="set">Custom_Product:0</Attribute>
    <Attribute name="Description" act="set">Test Epic Creation</Attribute>
    <Relation name="Scope" act="set">
        <Asset href="<Domain>/rest-1.v1/Data/Scope/189675" idref="Scope:189675" />
    </Relation>
    <Attribute name="StrategicThemes" act="add">
        <Value>StrategicTheme:5158</Value>
   </Attribute>
</Asset>

Here is what I am getting:

<Error href="<Domain>/rest-1.v1/Data/Epic">
    <Message>Server Error</Message>
    <Exception class="System.NotSupportedException">
        <Message>Cannot SetValue on Multi-value attribute.  Use AddValue and RemoveValue.</Message>
    </Exception>
</Error>

Problem I am facing is in setting the value of StrategicThemes attribute which is a multivalue attribute.

I am stuck. Kindly help.

Solution

This is because values can be added to multi-value attributes and cannot be set. Value is set only for single-value attributes. Also the code for adding values to the StrategicThemes attribute is incorrect.

<Attribute name="StrategicThemes" act="add">
     <Value>StrategicTheme:5158</Value>
</Attribute>

Thus the error in question.

The values for multi-valued attribute in should be added as:

<Relation name="StrategicThemes">
        <Asset idref="StrategicTheme:5158" act="add"/>
</Relation>