Which part?
"Saracens argued that the concept of a salary cap violates competition law rules (and is therefore illegal, void and unenforceable) because it prevented the club from being able to complete freely to attract the best players."
https://www.nortonrosefulbright.com...lay-in-sport-the-failed-challenge-by-saracens
Saracens did this after they were caught hiding payments.
Man City are arguing that the APT rules governing the market value of sponsorship deals are not legally enforceable. This is because the PL have gone after them over the 115 charges, amongst those are the allegations they artificially created sponsorship deals and hid costs to get around ffp & psr rules.