Why can’t I register for VoWi-Fi function when using Redmi Note 14 with Singapore Telecom SIM card?

This issue is due to recent changes made by the local carrier, Singapore Telecom, which require new adaptations in mobile phones.
For your reference, the detailed explanation is as follows:
1. The local carrier has updated its network settings or requirements, which is not yet fully compatible with the VoWi-Fi function on your device;
2. To resolve this issue, please upgrade your phone to the latest software version, which includes optimizations for better compatibility with the carrier's network;
3. For further assistance, please contact Singapore Telecom to confirm whether VoWi-Fi is available for your SIM card and phone model.