The most common and most likely answer to this crossword clue is the 10 letter word CARDHOLDER
I've seen this crossword clue in The Guardian
C
A
R
D
H
O
L
D
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R
Buddy explains!

The straight part
We know that "Paid-up member" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case paid-up member = cardholder.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 CARDHOLDER mean?
CARDHOLDER noun- A case for holding cards, as credit cards, bankcards, or business cards.
- An authorized user of a card used for financial transactions, etc.