A licence is essentially a contract between two parties. If you accept the licence (e.g by clicking on a tickbox, or proceeding with a download), then you are one of the parties to the contract. The other party is the person who is granting the licence.
Regarding the question of whether you are acting on behalf of your client in accepting the licence, that is a matter between you and the client. If the client instructed you to use a tool that was subject to a licence, or if you recommended to the client that you use the tool and the client agreed, you could argue that you were acting on the client's behalf, in which case it would be the client that was the party to the contract, not yourself.
In other words, it would depend on the circumstances of the specific case. Ultimately, it would be up to the courts to decide.
Really, this type of licence is no different from any other contract. Suppose you walked into a shop and bought a filing cabinet to use in a client's project. Would you be acting on behalf of the client in making that purchase? The same sort of test arises with software licences.