Custom analysers, you may need to create over the UI.
But in this case, your custom analyser requirement is already available as a prebuilt one.
Go over that analyser link shared in the previous (https://docs.couchbase.com/server/6.0/fts/fts-using-analyzers.html) and try to figure it out.
If you aren’t able to figure it out even after that, may be its a pointer to improve our documentation.
( I shall post the response after a while)
It seems passing ‘simple’ to the analyser should satisfy my case which is (unicode tokenizer+to_lower)filter.
However it seems there is no rest api to create a custom analyser with arbitary filters ,tokenisers etc.
We have to create analyser from console in those specific cases and use rest api to bind the analyser to the fts.