Partly right - the PSU itself is fine - capable of the needed voltage and current. However, USB-C PD3.1 requies a cable that matches the power you are using. The PD cables have a chip in them that tells the PSU & device being powered how much power it can deliver. Anything over 100w MUST use a PD cable.

Did the PSU come with a 240w PD cable? If not, are you using a regular USB-C cable - if so that is the problem.