At 11:57 UTC on 1st March 2019, automated tests indicated an issue with the TTS API for calls using text synthesis in our Washington DC Data Center. Customers with traffic routed through this data centre would have experienced silent calls. After all traffic was switched to the Singapore Data Center at 12:47 UTC, the issue was resolved for customers. A fix for the issue was applied at 13:11 in the Washington Data Centre and all traffic was returned.
An issue with the underlying servers processing the TTS API requests were unable to synthesise the text.
A program of work has been identified that includes improving the Text to Speech service.