How to: Exclusive OR for a mandatory choice?

[MartinHBramwell]

For what it’s worth :

V13 "Mandatory Depends On" documentation/guide wanted

So, I am trying to use your fix. The client side works after the tweak noticed by @iMoshi . Alas, the server side fails with: 04:57:40 web.1 | Traceback (most recent call last): 04:57:40 web.1 | File "/home/erpdev/frappe-bench-DYPW/apps/frappe/frappe/desk/form/save.py", line 21, in savedocs 04:57:40 web.1 | doc.save() 04:57:40 web.1 | File "/home/erpdev/frappe-bench-DYPW/apps/frappe/frappe/model/document.py", line 281, in save 04:57:40 web.…