Hey there, @helendevs! Thanks for contacting us. I’m happy to help you.
To confirm, the error message stops after “Reason:”, correct? Or does it show the reason?
Which payment gateway are you using? Is this issue happening with more than one payment gateway?
Furthermore, I’d like to understand your site properly. Please share with us the necessary information below for us to investigate the issue further:
System Status Report which you can find via WooCommerce > Status > Get system report > Copy for support.
Fatal error logs (if any) under WooCommerce > Status > Logs. Then you can use the selector to search for Fatal Errors.
You could copy and paste your reply here or paste it via https://gist.github.com/ and send the link here.
Looking forward to your reply.
Have a wonderful day!