Those Mutuel Prices are only available during the current race day. In your web browser, if you could go to TwinSpires toteboard for a track (either TwinSpires Mobile which requires no account, or login to the main TwinSpires) and get the Mutuel Results, then RDSS can get those Mutuel prices for that track and that day too.
RDSS gets its tote, scratch, mutuel prices and ProfitLine/Prime Power data from the publicly accessible
https://m.twinspires.com
Ted