"You were buying ice cream when you lost your wallet."

Translation: Kupowałaś lody, gdy zgubiłaś portfel.

[eviuszek]

Kupowałeś and zgubiłeś are also correct in this example.

[gizzard123]

It clearly specifies "your" wallet, so I wrote "... twoj portfel", and it was NOT accepted. If it was "...when you lost the wallet" then I would have written ".... gdy zgubiles portfel". Reported but I don't think they will bother responding.

[patriciawo972030]

I used swojego portfel

[alik1989]

Swojego is either genitive or masculine animate accusative, but portfel is masculine inanimate accusative, so we need swój in this sentence.