Of course I recognise it. It’s rather archaic today, but it’s still usable. Although we usually write it separated – “spolay ti”. Or sometimes it’s just “spolay”. Or “Spolay Bozhe” etc. It could be used as a thank you and as a wish for success to someone/thing.

Btw, when I searched for this, I found a thread in one BG forum on a similar topic, about the origins of “Blagodarya” and “Dovizhdane” (because “mersi” and “chao” are pretty clear). And, indeed, they also confirmed spolay ti is of Greek origin, while “blagodarya” is a Slavic calque (from Old-Bulgarian times) of the Greek evharisto, probably created by Cyril and Methodius or their students. So they were wondering what thankful expressions did we/Slavs have before Christianity – probably “zhiv i zdrav” and the likes. Likewise, the goodbye version “sbogom” also seems to be Christian in origin, as it’s probably a calque of the Latin “cum Deo” (with our “dovizhdane” being taken from the Russian “dasvidaniya”, which itself is a calque of the French “au revoir”).