# Digital text can be blocked

- Match the symptom.

## Sources and go deeper

- [Technical requirements PDF](https://documentation-be.five9.com/bundle/five9-technical-requirements/raw/resource/enus/five9-technical-requirements.pdf). vendor. last checked 2026-10. Fetched for this lab in October 2026. Re-read before you buy hardware or open a firewall.
- [ITU-T E.164, international public telecommunication numbering](https://www.itu.int/rec/T-REC-E.164). standard. last checked 2026-10.