The Smartlook session URL can be seen in the Smartlook section inside every crash report.

let config = BugsnagConfiguration.loadConfig()
config.addOnSendError { (event) -> Bool in
    let sessionUrl = Smartlook.instance.user.session.urlWithTimestamp
    event.addMetadata(sessionUrl, key:"Smartlook dashboard session URL")
    return true
}
Bugsnag.start(with: config)
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Full Bugsnag documentation with examples can be found on the official website.