Correct spelling for the English word "shooin" is [ʃˈuːɪn], [ʃˈuːɪn], [ʃ_ˈuː_ɪ_n] (IPA phonetic alphabet).
The word "shooin" is derived from the noun "shoo-in". The term originated in American English in the late 19th or early 20th century and initially referred to a fixed horse race in which one horse was ensured a win by fraudulent means, such as bribing other jockeys or intimidating competing horses. It was common for bettors to "shoo in" their favored horse, meaning they would guarantee its victory by various illegal methods.
Over time, the term "shoo-in" expanded its usage beyond horse racing and came to represent any person or thing that is practically guaranteed or destined to win or succeed, even without much effort or competition. The verb form "shooin" is simply a phonetic spelling of "shoo-in", often used in informal contexts or dialects.