Did you ever solve this by the way? Stuck on the exact same issue.
This should be easy. You would trigger a Pipeline when the child record is added or edited and the serial changes.
Then search for the parent record based on the field for related parent in your app.
The a For Each loop to update the serial. In practise there will only be one parent to update, arising out of the For Each Loop.
You're right - that was such a simple fix. Thank you! I was making it way more complicated 🤦♀️
Thank you both. I'll give that a try as well.
