Hi catarinacarraro,
Thanks for purchasing and using Meta Box Conditional Logic.
Sorry, this problem because Conditional Logic isn't compatibility with your PHP version, this is our bug and we'll have an update on the next day and you'll get the update shortly.
To fix it now, you can simply replace
['and', 'or']
with
array('and', 'or')
Then that line with become:
$relation = ( isset( $condition['relation'] ) && in_array( $condition['relation'], array('and', 'or') ) ) ? $condition['relation'] : 'and';
Thank you and best regards.
Tan Nguyen