Sorry, I'm a bit late to this thread and it may not be a valid observation, but surely the only things FedEx might have issues with are whether or not the nic base has child-resistant and tamper evident packaging, contains the other ingredients mentioned and is labelled correctly, as the other points don't apply because it isn't an eliquid. Or is there a definition of an eliquid somewhere in the FedEx small print which includes liquids which are unvapable in their current state, such as 72mg nic base?
I'm aware any liquid containing nicotine for sale for human consumption in the UK must be max 20mg/10ml, but the regs don't seem to be what FedEx are basing that message on; they specifically say eliquid (and include nic free eliquids in the 10ml max size, which isn't a requirement under the TRPR) -- except for the packaging, ingredients and labelling bit.