Bubble accepts 3 main body formats for API workflows:
"form-data"
"x-www-form-urlencoded"
"application/json"
If the data itself doesn't match the content type, the desired key-value pairs will not be parsed as expected. To fix this, you'll want to ensure that the body is consistent with the content type for the call.
For more information on API Workflows, check out our manual entry here.