SSL certificate client authentication fails with "Certificate has expired"

Hello, I’m using 2 way (mutual) authentication to call an API of a payment gateway, I added the crt and private key files to settings->certificate. but when I call the API I always get 403 forbidden and “certificate has expired” response. here is a screen shot:

I also tried to add a pfx file I created for the cert, but also without luck.
what is the problem and how to fix it? thanks.