You have several options when sending a Payment Request
Authorize Full Amount: This will send an authorization to the gateway for the full amount and will appear as an authorization in Salesforce
Authorize Minimum Amount: This sends the very minimum authorized amount allowed by the card network (Visa, MasterCard, American Express, etc..) and will appear as a voided transaction in Salesforce
When you authorize a minimum or full amount, please keep in mind that you will need to process the complete transaction showing the full amount. When the transaction is created it will authorize and void the minimum amount the gateway allows.
For more information on using these fields please check out the Payment Request Configuration Article