Hi,
Did you confirm you have already correctly renewed the SSL certificate?
IIS 7: Renew a certificate
https://sg.godaddy.com/help/iis-7-renew-a-certificate-4802
Also, please check if below articles could help resolve your issue.
Remote Desktop Gateway SSL Error, or Network Access Protection LIES!!!
https://windowsserveressentials.com/2015/01/23/remote-desktop-gateway-ssl-error-or-network-access-protection-lies/
SBS, Essentials, RWA and SSL
https://windowsserveressentials.com/2013/02/01/sbs-essentials-rwa-and-ssl/#gateway
Thanks,
Eleven