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For the Subscription URL field, a default value should be displayed next to the field. That value should be ' (Default: sip:~rl~C~xxx@sipdomain~~rl~C~xxx@sipdomain.tld), where ' xxx ' is replaced with your extension, and ' sipdomain.tld ' is replaced with your SIP domain. Copy and paste the '~rl~C~xxx@sipdomain~~rl~C~xxx@sipdomain.tld ' entry in the default hint into the Subscription URL field.
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