How can you update a single value dropdown via Web Services API (WS API)
the first step would be to get the object ID of the attribute that you're wanting to update. This is probably the most complicated part because it requires delving into the schema. We have a KB here that you can follow to find fields in the schema: https://ca-broadcomcsm.wolkenservicedesk.com/wolken/esd/knowledgebase_search?articleId=223719
So, for example, here we have a custom field called "DropDownList". In order to work with the values for this dropdown list, we'll need to first grab the _ref:
To get the AllowedValues, you would append /AllowedValues to the object ID I have circled above: https://rally1.rallydev.com/slm/webservice/v2.0/AttributeDefinition/<OBJECT_ID>/AllowedValues
In this list, you can see the individual values in the dropdown and their associated object IDs:
Using these object IDs you can perform standard update and delete operations.
For example, to delete "Beta" in the above list, make a DELETE method call to: