Comments by Member 16112833 (Top 3 by date)

> The underlying connection was closed: An unexpected error occurred on a receive.
Something is improper with the request at the network level, it isnt hitting the BW API, otherwise you would get an HTTP response code of some sorts

This may be the issue
https://stackoverflow.com/a/37219622

Depending on your os behavior it may be trying to send with TLS1.0 which Bandwidth does not support, TLS1.2 should work

edit: adding this line inside SendSMS() might be the fix you need

System.Net.ServicePointManager.SecurityProtocol = DirectCast(3072, System.Net.SecurityProtocolType) 'TLS 1.2

it could be, but id need to know the error.

Did you change the 5500000 in the URL to your accountId? That would cause a 401