We got the below while sending SMS from Click Dimension. We were using Bulk SMS as our SMS connector for Click Dimension.
When we opened the Text Messages record we figured out that we were getting “The remove serve returned an error (403) Forbidden.
This occurred because we had our credit with Bulk SMS already consumed.
The issue got fixed when bought the credits again with Bulk SMS.
Hope it helps.
Nishant Rana's Weblog 