Hello @Earplug ,
You still have not supplied the backup as requested so we have no way verifying what your configurations contain.
I tested this briefly with an 8200 and the USB dongle on a VVX 350 running a currently supported software 6.3.1 or a VVX 450 running 5.9.4.3247 with the following configuration:
<web voice.volume.persist.usbHeadset="1"/>
Once the Volume is adjusted it stays like this until the phone is rebooted.
If this fails, and no other community volunteer has any other ideas the next step would be to contact your Poly reseller.
Our records show this phone was sold via NETXUSA INC back in 12/8/2020 and they would be your Tier 1 support.
In order to raise a support ticket, you need to work with your Poly reseller as they may need to do this for you.
End Customers are usually unable to open a ticket directly with Poly support. Available End User Poly services offerings are detailed here
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Best Regards
Steffen Baier
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The title Polycom Employee & Community Manager is a community setting and does not reflect my role. I am just a simple volunteer in the community like everybody else. My official "day" Job is 3rd Level support at Poly but I am unable to provide official support via the community.
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Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels.
Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's
