Heya,
I've had this problem for aaages now but only now bothered to actually ask how to fix this 😅 Just stopped using it so far.
When asking Alexa something like "close blinds" she responds with "Okay" but doesn't actually do anything. Telling her to "turn blinds off" works (since HA reports it as an on/off button to Alexa).
However telling Alexa to "set blinds to X percent" she responds with "I don't know what went wrong", however setting the percentage in the Alexa app does actually close/open the blinds to the set percentage.
What could cause this weird behavior? Thanks already for your answers!