I am unable to use the keypad during a call to navigate thru voice instructions

Re: "Iphon15 will not let the user select numerics to navigate voice prompts during a call with any support".

Updating to the newest iOS18.2 version may be helpful. (Wise to back up all data first)

ie: Settings > General > Software updates.

If iOS 18.2 is already installed, try re-starting your iPhone: (ie: deletes temporary files, re-establishes connections, may update recent setting changes, and often restores order if something is not working as expected.)

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Else: if you still need help:

✽ You might want to check if you have any content and privacy restrictions set in ScreenTime :

✽ Sometimes third-party (non-Apple) apps (even VPN) may cause interference:

Try turning off or deleting any that aren't necessary.

For any that you find necessary: try updating them to the latest version.

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✽ If needed: You can try contacting Apple Support:

There's a "Support" link at top right, and one at bottom left, on this discussion page.

or

See a list of Apple phone numbers around the world : Contact Apple for support and service - Apple Support

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I notice the author who posted the setting change (in the linked discussion thread you provided) said it worked for incoming calls on an iPhone 13 Mini running iOS 17.4.1. ... and also requested:

"If this works for you, please reply and confirm. If not, please give details which will help us reach a solution."