Selling monetary vouchers in terminal is very similar to selling normal products with one difference.
As usual open up sell a product
Then select monetary gift voucher or whatever the name of your monetary product is.
Personalisation and enhancements (if added) are still available and monetary vouchers provide the same options as normal products.
Then select your value, if you have customer enters value, you will need to input the amount yourself.
If your product has set options you will need to select the option you would like.
The process after this point is exactly the same as a normal product on terminal. To see this process in full please go here