Fix config URL so that the phones don't get an invalid URL when $domain_name is unset. They would previously receive `/app/provision` with no domain/ip included, which makes the phone unable to provision again once they have been added to the Devices page without manually re-setting the config URL or factory defaulting the device.
The alternative solution is that the PHP code could always ensure that the $domain_name variable is set even if the device doesn't exist. My suggestion is to see if it can be set to the same domain/IP as the original provision request from this unconfigured device
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