Hi @jona12, the @postpromoter bot (like all other bid-based bots) are based on a bidding system. This means the vote value is based on the amount of SBD/Steem that is bid in each voting round. Some rounds you might have a slight loss and some you might have a slight gain. Overall it's pretty close to break-even which it sounds like it is in your case as well.

Also please remember that the payout value fluctuates as the value of STEEM changes in the markets, so your actual return will not be determined until the post pays out.