My changes are in lines 291, 292, 304, 331, 343. I basically added a ref to the select to keep track if the selected id, if there was none (the default option has value undefined cause its out of the .map) then I added a second case in the disabled prop.

This is one way to do it, but it duplicates logic. I was hoping to align this behavior with the validation we do in the action. When the form is submitted it returns an error; when that error is not a ConflictingSkillsError we are unable to submit a valid copy action and could thus disable the confirm button. Doing something like that would prevent having to separately code-up all validation logic in our frontend state.

This probably means we have to call validate() not onChange but on another trigger.

I changed this to match your validation errors: it starts in line 132, 153, 320, 352 and 388. So basically if the target client doesn't exist or is empty it throws a validation error.

I feel that combined with the warning this works quite well, but let me know what else I can do better.

That's a good improvement already! I still have something nitpick about;

CopyAction.decode is actually already doing the validation you're doing on line 153-4; alongside checking some other fields. Those errors end up in the first foldW callback, directly beneath it. It would be nice to re-use those errors. Perhaps they can be wrapped in a ValidationErrors type, or something like that, to have something to check on in our Modal component.

If you think this is a bridge too far, it's also oke to leave it like this.

Is this more in line with what you thought? I see that the errors can also contain a message so I allowed for it to be passed within the ValidationError. Lines changed ad 147 for the Error extension and 171 to 179

This looks good! Probably need to do something about the different approach in ConflictingSkillsError, which is not class based, but that's something for the cleanup part.

great will push shortly and then think about the ConflictingSkillsError, so we can align them a bit.