This is a good place to start https://documentation.meraki.com/MX/Client_VPN/Troubleshooting_Client_VPN Error 691 Possible causes and solutions: Invalid user credentials Solution: Confirm user credentials are correct. When using Meraki authentication, usernames should be in e-mail format (ex. user@example.com). When using AD or RADIUS authentication, be sure to enter the username in a format that will be recognized by the server, including the domain if needed (ex. DOMAIN\user). User not authorized Solution: If using Meraki Authentication, ensure that the user has been authorized to connect to the VPN. No certificate on AD server Solution: If using Active Directory authentication with Client VPN, make sure the AD server has a valid certificate for TLS. Incorrect DNS name resolution from the MXs upstream DNS server Solution: If the MX is configured with an ISP DNS server, change this to a Non-ISP public DNS server such as Google 8.8.8.8 Alternatively, this message can be caused when a mismatch of pre-shared secrets between a RADIUS server and MX results in bad encryption of the password. Test this by changing the pre-shared secret in Dashboard and for the RADIUS client on the server to something simple, such as "Meraki". If the error disappears, verify the secret used is correct on both devices, and simplify the password if needed.
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