Github search API - Get closed and unmerged PR

Hi, i’m using github search API with the following query: org:my-org+is:unmerged+is:closed+is:pull-request+created:2021-04-01..2021-04-30, but the result is MERGED PRs, instead of PRs closed but unmerged. If I use the operators in github.com the results are correct. am i missing something here?