Unable to update order tag price when tag value has a prefix applied

I’m trying to divide the order tag price by 2 when the tag value is prefixed by “left” or “right”.

Checking for the prefix and getting the parent price works just fine. However, when I try and use the “Update Order Tag Price” action, it fails on tags with a prefix.

If I update an order tag without a prefix, the half-price is properly set.

In the following I have configured two action both updating as price / 2.

2021-12-29_16;32_1640817154_%pn

The popup is displaying [=TN('[:ParentPrice]') / 2] which is the same expression used to try and set the tag price.

action to update if prefix is present:

test action to update order tag with no prefix (this works, ignore price: 0 in the popup as it’s showing parent price, not order tag price):

any suggestions?

TIA