I have added a custom field on the order profile settings. Now I want to pass that custom field to the final checkout page. I have added the field as a parameter on the payment system. But the parameter is not passed to checkout page?!
If I " click here här to see all available variables you can pass to payment system. " I see the parameter {field1}. Is that the name I shall use, or is it the name I gave to the custom field. I have tried everything, but I dont get it to work. Am I doing something wrong?

Have you got the syntax right,?
In my 3.5 system the custom fields have an underscore - {field_21} ?
 
Broadly you use this custom field to pass the data collected in it from the form to any other parts of the store, for example in my case {field_21} captures and contains the customers delivery instructions and these are passed to the email system to notify the administrator and to the customer, as well as being used on the packing slip for the couriers information.

Yes, it is an underscore, I mised that when I wrote. Do you use the brackets {} when you using the parameter?

Yes you do