elasticsearch - forward slash issue in ELK query strings -

i have elk query in query_string looks like:

{"query_string":{"query":"context.productname:abc/def"}} 

this fails.

but, following works:

{"query_string":{"query":"context.productname:abc\\/def"}} 

lets have value in variable like

let productname = 'abc/def'

what right way escape variable works elk query?