*Please note you need an admin account to do this.
1. Check if Scan to Salesforce is installed at Connected Apps OAuth Usage.
SETUP > Apps > Connected Apps > Connected Apps OAuth Usage > scroll to Scan to Salesforce
If you see the Uninstall button at Scan to Salesforce, the setting is complete.
If you don't see it, click Install to install Scan to Salesforce.
2. After checking step 1, relax the restrictions as follows:
SETUP > Apps > Connected Apps > Manage Connected Apps > Edit Scan To Salesforce > Relax IP Restrictions