Is "brave" an adjective or adverb?


I saw an ads with a slogan somewhere on my way home yesterday:

“Why can’t you act brave and confident to buy it?”

Is it really grammatically correct to say “act brave and condifent” instead of
“act bravely and confidently”?

‘Act’ can be considered a linking verb here-- meaing ‘act like a brave/confident person’. You are right, though, that the adverbs are better choices. We can see by the rest of the sentence that the writer is not very good. It should more naturally read: ‘Why can’t you act bravely and confidently and buy it?’

Thank you so much for the help, Mister Micawber!