Websockets endopoints for testnet.binance.vision do not respond

Hi,

I am struggling to connect to websockets on the testnet.binance.vision. The websockets work without any problem for binance network, but for development purposes I need to communicate with the sandbox.
According to this documentation: https://testnet.binance.vision/, I should just replace wss://stream.binance.com:9443/ws with wss://testnet.binance.vision/ws and it should work but for some reason it does not, i.e.:

pj@pj-desktop:~$ websocat wss://stream.binance.com:9443/ws/bnbbtc@depth
{"e":"depthUpdate","E":1610292416671,"s":"BNBBTC","U":1184182347,"u":1184182355,"b":[["0.00108960","47.70000000"],["0.00108890","187.28000000"],["0.00108800","1.50000000"],["0.00108790","187.29000000"],["0.00108680","5.44000000"]],"a":[["0.00109130","97.75000000"],["0.00109140","450.50000000"],["0.00109260","1.12000000"]]}
{"e":"depthUpdate","E":1610292418671,"s":"BNBBTC","U":1184182407,"u":1184182437,"b":[["0.00109000","3.64000000"],["0.00108990","9.55000000"],["0.00108920","159.06000000"],["0.00108850","176.13000000"],["0.00108800","502.05000000"],["0.00108740","5.44000000"],["0.00108720","0.00000000"],["0.00108210","8.37000000"],["0.00108190","1.15000000"],["0.00106410","30.19000000"]],"a":[["0.00109040","1.62000000"],["0.00109050","9.31000000"],["0.00109060","0.00000000"],["0.00109160","186.30000000"],["0.00109230","10.60000000"],["0.00109290","121.90000000"]]}
...

pj@pj-desktop:~$ websocat wss://testnet.binance.vision/ws/bnbbtc@depth
<no response, it just hangs>

I have also tried with different tickers but it does not change anything, it looks like the endopoint address is incorrect.

Does anybody know what is the issue here?

“bnbbtc” doesn’t have enough liquidity; please try bnbusdt

It looks like itr works for bnbusdt:

websocat wss://testnet.binance.vision/ws/bnbusdt@depth
{"e":"depthUpdate","E":1610357900082,"s":"BNBUSDT","U":2654553,"u":2654556,"b":[["39.58690000","2.03000000"]],"a":[["39.60920000","0.00000000"],["39.61170000","1.70000000"]]}
{"e":"depthUpdate","E":1610357901082,"s":"BNBUSDT","U":2654557,"u":2654560,"b":[["39.58740000","2.40000000"],["39.58690000","0.00000000"]],"a":[["39.60260000","0.00000000"]]}
{"e":"depthUpdate","E":1610357902082,"s":"BNBUSDT","U":2654561,"u":2654566,"b":[["39.58740000","0.00000000"],["39.58510000","0.28000000"],["29.82300000","0.00000000"]],"a":[["39.59430000","0.00000000"],["39.61170000","0.00000000"]]}
{"e":"depthUpdate","E":1610357903082,"s":"BNBUSDT","U":2654567,"u":2654568,"b":[["39.56560000","10.78000000"]],"a":[["39.59110000","6.13000000"]]}

Thank you!