Visa Necessary To Sell Books At A Book Fair Abroad?

I'm from the UK and considering exhibiting at a book fair in Lithuania next year, to promote my recently published book. The problem is, am I violating any laws/restrictions if I sell my books at the fair? I would be travelling on the 90 day schengen visa that we have by default in the UK.

It's not exactly like I would be employed in another country, I'd just be sat at a stall with copies of my book and giving them out in return for money. But at the same time, it's generating money in another country, so I'm left a little confused where this sits legally, if I would need some sort of specific work visa to do events like this abroad.

Thanks for any help you can give!

(I posted here and not the UK legaladvice reddit because I figured this is more tailored towards EU/Lithuania law than in the UK)