In a nutshell.
a) wait a day or two more, drop them a message/invoice politely checking if there’s a problem
b) end of the week, put in a non-payment claim – it’ll take 2 weeks while eBay wait in case the buyer does cough up then it’ll refund your fees. If the buyer does click on the button to admit non-payment then it’ll be quicker – rarely happens
c) Put buyer on your blacklist of people you won’t sell to
d) relist
e) Sigh and huff a bit.
Not much else you can do. ‘Technically’ I’m sure someone will probably come along say you can take them to small claims court for non-payment blah blah blah.