Voice to Text on a Beta platform

I'm writing an app that uses on-device voice to text for recognising scientific terms. It works fine on my phone but now in beta my first tester cannot make it work. All the permission requests are working: p&s Mic and Speech Recognition are both now enabled on the target device where the user granted the app permission. Is there something else I'm missing? Incidentally, both my phone, the target phone and my XCode are fully up to date. Thanks.

Voice to Text on a Beta platform
 
 
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