I bought a cheap ticket to KL within 60 days,I was asked by Singapore air at UK airport if I had a ticket, but they didn’t want to see it, same at BKK immigration, they asked when I was flying out, but didn’t want to see my ticket.
I had an onward flight, Singapore air asked if I had one, but didn’t ask to see it. My friend flew with Turkish air and was made to purchase an onward flight online before he was allowed to fly, it’s all a bit hit and miss, but better to have some form of cheap onward travel, even if you don’t intend to use it.