The request was aborted: Could not create SSL/TLS secure channel error on check out

I'm getting The request was aborted: Could not create SSL/TLS secure channel error on check out with FedEx plugin.
Version 4.0.
It's happening in prod only and fine in test and dev.
Any suggestions how to fix it.
Thank you so much
Len

Has it just stoped working ?
or Does you production server have the correct version of SSL/TLS installed ?

It stopped working. what should I check on prod server?
Thank you

Recently I had two clients using UPS that were getting that same error.  What worked for them was to use IISCrypto and click the “best practices” button and then restart the server.

Still not working.
It's FedEx plugin.
Thank you

Did you  disable the protocols TLS 1.0 and TLS 1.1 via the IISCrypto GUI?
Did you reboot the server?
(Then I recommend again run IISCrypto and check to be sure  TLS 1.0 and TLS 1.1 are not still enabled.)

It works now.
Thank you so much for your help!!!