How to use blockstream's REST api to retrieve JSON output on an address? I have a bitcoin address and I want to get the JSON format of the balance using blockstreams api service. 

It's this one: https://github.com/Blockstream/esplora/blob/master/API.md#transaction-format

It's not clear on what I need to put in the URL. I tried: 


  https://blockstream.info/address/:bc1xxxxxxx


and it doesn't work.
As others have said you can use https://blockstream.info/api/address/bc1qgsmfaz22lzy08wqjspd8xtm43hal5tgz4hyac6 for the JSON - the doc is in reference to running a local instance - the exact endpoint is depending on deployment, the default deployment we use has nginx forward /api/ requests to electrs without the api bit https://github.com/Blockstream/esplora/blob/master/contrib/nginx.conf.in#L32 but it depends on how people want to deploy it.

We should probably mention this in the API.md file to avoid confusion