The “compensation” was paid to their owners, not to the slaves. There are archival records of women being paid for the use of their slaves. Just as they would be paid for use of their mule.

btw, This same record appears in slave work done by blacks rebuilding the Mississippi River levees after the great flood of 1927. The people were fed and given tents during the rebuilding. The landowners were paid. That resulted in the NAACP rejecting Hoover in 1932 and endorsing FDR, the first time they ever endorsed a Democrat.