Can't authorize Mac for iTunes

i got new mac , decided set itunes account. signed in apple id , plugged in iphone transfer purchases iphone itunes. when try so, says nothing can transferred because "am not authorized them on computer." hit "store" , "authorize computer" told me to, , tells me computer authorized! it's endless cycle of on , on again. do?

 

why don't unauthorise computers , start again? takes 2 mins...

 

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