The most common and most likely answer to this crossword clue is the 8 letter word ACCEPTED
I've seen this crossword clue in The Daily Telegraph
A
C
C
E
P
T
E
D
Buddy explains!

The straight part
We know that "Sanctioned" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sanctioned = accepted.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 ACCEPTED mean?
ACCEPTED verb- To receive, especially with a consent, with favour, or with approval.
- To admit to a place or a group.
- To regard as proper, usual, true, or to believe in.
- To receive as adequate or satisfactory.
- To receive or admit to; to agree to; to assent to; to submit to.
- To endure patiently.
- To agree to pay.
- To receive officially.
- To receive something willingly.
- Generally approved, believed, or recognized.