VSLEndpoint.m

pj_activesock_enable_iphone_os_bg(PJ_FALSE);
[self createPoolForPJSIP];

I added " pj_activesock_enable_iphone_os_bg(PJ_FALSE);" above "createPoolForPJSIP". It's working.

Podfile

`# Uncomment the next line to define a global platform for your project
platform :ios, '13.0'

target 'VialerSIPLib_Example' do
#use_frameworks!

pod 'VialerSIPLib', "3.7.3"
pod 'SPLumberjackLogFormatter', :git => 'https://github.com/VoIPGRID/SPLumberjackLogFormatter.git'

end

pre_install do |installer|

workaround for CocoaPods/CocoaPods#3289

Pod::Installer::Xcode::TargetValidator.send(:define_method, :verify_no_static_framework_transitive_dependencies) {}
end

post_install do |installer_representation|
installer_representation.pods_project.targets.each do |target|
target.build_configurations.each do |config|
config.build_settings['ONLY_ACTIVE_ARCH'] = 'NO'
config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] ||= ['$(inherited)']
config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] << 'PJ_AUTOCONF=1'
config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '13.0'
end
end
end
`