Fail to acknowledge there is no spa in Singapore (6)
I believe the answer is:
ignore
'fail' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ignore that I've seen before include "Walk away from" , "Send to Coventry" , "Intentionally disregard" , "Discount" , "Dismiss" .)