you cant directly put computer group under computer name or ID, it should be passed under relevance filed of your xml with your computer group ID something like below & remove any target entry as well than push xml from API.
<Title>My Test Action</Title>
<Relevance>exists true whose (if true then (member of group 1177 of sites) else false)</Relevance>
OR
<Relevance>exists true whose (if true then (member of group 1177 of site "XYZ") else false)</Relevance>
OR
<Relevance>member of group 1177 of site "XYZ"</Relevance>