I think vault version has to be 3.5 or above for c... @yearnfinance

Answer: Yes, it appears that vault version 3.5 or above is necessary for cowswap swaps. This is because cowswap swaps require a specific set of features that are only available in the 3.5 or higher versions of vault. This includes features such as the ability to transfer tokens between two different vaults, as well as the ability to securely store and manage the underlying assets. In addition, cowswap swaps require a high level of security, which is provided by the latest versions of vault.

seems to work.