In sales volume it shows $0 for accrual but in verification level it shows accrual of $5.85. The pay button shows $0.
If sales volume showing $0 and Verification level is showing $5.85 means definitely there must be Partial settlement done for that $5.85 amount.
Please go to VBo2 ->goto Rebate payments-> click on Rebate document-> there if you observe either credit memo request or Credit memo for $5.85 then my guess is correct.
If the above of my guess is correct then you can not do any partial settlement since it is already done the partial settlement.
Please check and update.
thanks,
Srinu.