For anyone experiencing the same issue, I found a work-around.
Turns out that the cause of this mismatch of properties is due to the additionalProperties.
Instead of using an object with key:value, I made an array with objects that have { key, value }, and now it seems to work!
In the end, the error is misleading, and perhaps eventually they will support additionalProperties, but in the meantime, I would advise to avoid it!