fundRaising Manager supports multiple ways to prevent an Opportunity from being receipt eligible. Below are different mechanisms which can be used prevent recceipting.
Non-Eligible Campaign
A Campaign can be configured with a Type value of Non Eligible. Any Donation made a to Campaign with this value will not be receiptable.
Campaign with 100% Benefit
Any donation made to a Campaign with an associated benefit of 100% will not ne receiptable.
Not Eligible for Receipt Override
Intended for Imported Data from other systems, this override field overrides any other state on the Opportunity and prevents a Donation from being receipted. If the field is not present in the Opportunity layout, your Administrator or cloudStack can add the field to the System section of the Opportunity layout.