XQuery [value()]: ‘value()’ requires a singleton (or empty sequence), found operand of type ‘xdt:untypedAtomic *’

A co-worker had tackled a similar problem before. Here is what we came up with. NOT intuitive!

insert into PurchaseDetails
(Upc, Quantity, PurchaseDate, PurchaseCity, PurchaseState)
select
    pd.value('Upc[1]','char(11)'),
    pd.value('Quantity[1]','int'),
    pd.value('PurchaseDate[1]','varchar(7)'),
    pd.value('PurchaseCity[1]','varchar(50)'),
    pd.value('PurchaseState[1]','char(2)')
from @xmlData.nodes('//Database/PurchaseDetails') as x(Rec)
cross apply @xmlData.nodes('//Database/PurchaseDetails/PurchaseDetail') as i(pd)