IN operator not working for assets

[LeanderFS]

While developing an importer for the assets I've bumped into a rather strange issue. The docs (GET THE LIST OF THE ASSETS OF A GIVEN ASSET FAMILY ) state that the endpoint supports filtering based on an asset code. But for some reason the stated syntax doesn't work with the API client.

For instance, the following url will always return an exception.
https://[instance-name].cloud.akeneo.com/api/rest/v1/asset-families/[asset-family-code]/assets?search=%7B%22code%22%3A%5B%7B%22operator%22%3A%22IN%22%2C%22value%22%3A%5B%221200x1200%22%2C%22vooraanzicht_2%22%5D%7D%5D%7D

{"code":422,"message":"The search filters have an invalid format.","errors":[{"property":"","message":"The property code is not defined and the definition does not allow additional properties"}]}

If I urldecode this uri it has the exact same syntax as the docs (here) show:
https://[instance-name].cloud.akeneo.com/api/rest/v1/asset-families/[asset-family-code]/assets?search={"code":[{"operator":"IN","value":["1200x1200","vooraanzicht_2"]}]}

Seems like something is not quite working, or I'm not understanding the docs.