From Longman Dictionary of Contemporary Englishmany happy returnsmany happy returnsused to wish someone happiness on their birthday → happy
Examples from the Corpus
many happy returns• Next up we would like to wish birthday girl Fiona many happy returns.• They went for more, but Nicky Hammond in the Town goal made sure they didn't have too many happy returns.• Charlotte will be wished many happy returns by family and other visitors to a nursing home in Redcar, Cleveland.• And, no doubt about it, very many happy returns, sir. 