Hello@Alberto_Umana 
Thank you very much for you response.

I was able to solve it on my side. The issue was lying on snowflake side. I realized I had to not only grant USAGE permission but also OPERATE permission to my snowflake account. Also added sfRole to the connection. After renewing connection, recreated the external table one more time and it worked on my side. 

CREATE CONNECTION snowflake_connection1 TYPE snowflake
OPTIONS (
host '<hostname>',
port '<port>',
sfWarehouse '<warehouse-name>',
sfRole '<role-name>',
user secret ('<secret-scope>','<secret-key-user>'),
password secret ('<secret-scope>','<secret-key-password>')
)