A ProductPartition of type SUBDIVISION must always be completely partitioned, so all child nodes of a subdivision must have a
caseValue of the same type, and every subdivision must contain an "other" node. Please note that, each subdivision must contain an "empty" caseValue of the correct type, representing "all other values". You may check this
guide for reference.
Upon checking on your request log and since you are going to create a root product group, what you need to create is the root product partition with UNIT as
partitionType. You may refer to this
link for sample SOAP request on how to create a product partition with just the root node.