How to block being able to confirm a document using serverless extension

We've tried to block the possiblity to confirm a document from several events without result yet. What we tried :

Add a custom error message
Take a field type score and set the value of rir_confidence below the threshold
Here's the documentation we based our trials : https://developers.rossum.ai/docs/automation-rules-overview

Is there a way to that using serverless extensions ?

Thanks