What's the difference between 恭喜發財 and 恭禧發財? Today I visited a house that had Chinese New Year banners all over. On the stairs, one banner reads 「恭禧發財」, and above a door, another banner reads 「恭喜發財」. Both of these are pronounced exactly the same in Cantonese and Mandarin. 

Questions:


What are their differences in terms of meaning? 
Which is 'correct'? (i.e. Which is the canonical or most popular version?)
When people say 「gung1 hei2 faat3 coi4」 / 「gōng xǐ fā cái」 during Chinese New Year, do they mean 「恭喜發財」or do they mean 「恭禧發財」?
The correct way to write the phrase is「恭喜發財」. This phrase is made up of two words:


「恭喜」, meaning congratulations;
「發財」, meaning to make a fortune.


In contrast,「恭禧」is not actually a word. At most,「恭禧發財」can be viewed as a pun which emphasises the fortune aspect of the phrase, as「禧」(good fortune) is a homophone with「喜」.