You can use CiviCRM without using the Membership module at all, or you can add free Memberships.
That said, I may be mis-reading your comment. CiviCRM is free open source software, so there is no 'you must pay to use civicrm' but there are often costs associated with 'freedom' namely hosting, specialist configuration, etc but there is no 'user fee' per se ...
Thinking out loud, but I think that the idea of using a wallet payment processor is a good lead.
Maybe something along the lines of:
Record a payment for the user
Then record a credit note
Create a payment processor which uses the credit notes.
I have to admit that refunds/credits is something that is sometimes not very well defined in CiviCRM, so I'm not ...
The problem is solved by using cf-civicrm developer version from github rather than the version proposed by Wordpress.
To understand more you can see this Post : https://github.com/mecachisenros/cf-civicrm/issues/185
Welcome to SE CiviCRM, The question you raised is basically for Authorize.net support team instead here. You will need to contact Authorize.net support team to change the currency for your merchant account.