Resolve the paradox. Two facts are presented as both true, and they seem to conflict: the average amount spent per recorded transaction went up, yet total revenue went down. A correct resolution must be consistent with both facts at once and supply the hidden distinction that lets both be true without contradiction. The key is that the per-transaction average is computed only over the transactions that still happen, while total revenue depends on how many customers there are in the first place.
Why (D) is correct: if many former customers who made small purchases left because they would not use the app, then two things follow at the same time. First, removing the small-basket shoppers raises the average of the remaining transactions, which matches the rise in spending per transaction. Second, losing a large group of paying customers removes their purchases from the total, which matches the decline in revenue. One hidden change, the loss of low-spending customers, explains both facts without disputing either.
Why the others fail:
(A) explains only the higher spending per transaction. It leaves the revenue decline unexplained and in fact predicts higher revenue, so it addresses just one side of the puzzle.
(B) tries to resolve the tension by claiming the reported per-transaction figure was overstated. That denies a fact the problem gives as true; a resolution must accept both facts, not erase one.
(C) raises costs, which is consistent with both facts but irrelevant to them. Costs affect profit, not the question of why revenue fell while per-transaction spending rose.
(E) would lower the amount spent per transaction on frequently bought staples, which pushes against the stated rise in spending per transaction. It deepens the discrepancy rather than resolving it.
The answer is (D).