The most common and most likely answer to this crossword clue is the 13 letter word PAY-AS-YOU-GO
P
A
Y
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A
S
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Y
O
U
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G
O
Buddy explains!
The straight part
We know that "Plan/to spend a penny?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plan/to spend a penny? = pay-as-you-go.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PAY-AS-YOU-GO mean?
PAY-AS-YOU-GO noun- A financial policy by which capital projects are financed from current revenue in the operating budget rather than through borrowing.
- A payment method where credit is purchased in advance, used in small amounts and topped up when required. Used especially of mobile phones and transport ticketing.