Busy tone heard when dialing to iphone over Volte

[lycaesar]

Please tell us some basic information before asking for help:
Model Name: ASUS_X00TDE
Firmware Version: PKQ1.WW_Phone-16.2017.2002.061-20200219
Rooted or not: No
Frequency of Occurrence: Always
APP Name & APP Version (If your issue relates to the app):
In addition to information above, please also provide as much details as you can, e.g., using scenario, what troubleshooting you've already done, screenshot, etc.
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When VoLTE is turned on, everytime i make call to iphone, i will hear busy tone and i will cancel the call. However, the called side actually rings and can answer the call if i do not cancel the call

[Y_ASUS]

Hi lycaesar,
Could you tell us the carrier?
Please also check your PM for a message I have sent you. 
Thank you 🙂

[lycaesar]

Y_ASUS

Hi lycaesar,

Could you tell us the carrier?

Please also check your PM for a message I have sent you. 

Thank you 🙂

View post

I have replied you PM. Thanks

[Y_ASUS]

Hi lycaesar,
Thank you for waiting. A new firmware update has been released and improved the behavior. We suggest that you download this version WW-16.2017.2007.084. You may manually download from our website, or check update in Settings > System > System update.
https://www.asus.com/Phone/ZenFone-Max-Pro-M1/HelpDesk_BIOS/
How to update firmware on my phone? | Official Support | ASUS Global
Thank you🙂