If you want to add a second bounty, you will have to add a bounty of double the value of your previous bounty. Since that appears to have been a bounty of 200, your new bounty should be 400. You don't have enough rep left to do so.
Given that you actually set a bounty of 400 but did not award it, half of it got awarded to the eligible answer given the conditions outlined in "How does the bounty system work". (Which explains the bounty value of 200 I mentioned before)
Twenty-four hours after the end of the bounty period, if the bounty
starter has not manually awarded the bounty, an eligible answer can be
automatically awarded half the bounty amount. The criteria for an
answer to be eligible for automatic awarding are as follows:
- The answer must be given after the bounty was started
- The answer must have a score of at least +2 If two or more eligible answers have the same score, the oldest answer is awarded the bounty.
The 400 bounty does suggest that, even if you had enough rep to do so, you will no longer be able to set another bounty on the question. 500 is the maximum if I recall correctly.