curl -X POST -v -u Administrator:password “http://10.106.21.147:8093/query/service” -d ‘statement=CREATE INDEX idx_test ON testBucket’
Which server version are you using? Which edition (Community or Enterprise)?
while creating an index you either need to specify if it is a primary index or a set of secondary keys on which the index needs to be created.
I can see missing secondary key part in the statement above.
If the problem persists, please check out query.log or indexer.log for any errors.