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When you receive a contact request from another XING member you can choose to either accept or decline it. If you confirm the request the other member will see under Network that you are now connected. The other member will not receive any notification if you decline however.
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In the XING App you will be notified unter Notifications (bell icon) if you have received a new contact request. The app can also send you an additional push notifcation about a new contact request if you allow that in your settings.