This setting is used for situations in which OnBase Healthcare Form Manager must validate URLs containing legacy checksums. Legacy checksums are checksums that were generated before the ChecksumKey setting was available in the Healthcare Form Manager web.config file. Legacy checksums may be required for certain OnBase environments, such as an environment where multiple versions of OnBase are used (an Incremental Parallel Upgrade Process, or IPUP, environment).
If your solution needs to support Healthcare Form Manager URLs with legacy checksums, set the EnableLegacyChecksumFallback setting to true to validate checksums using the legacy method. This should be considered a temporary method of validating legacy checksums until you can re-create and replace the existing URLs using a unique string value as the checksum key.
If the EnableLegacyChecksumFallback setting is false, then all checksums used in Healthcare Form Manager URLs must be generated using the specified ChecksumKey value.