You want to enhance the UI screen with different functionalities, e.g. adding rules with the Key User Rule Editor. What options do you have?
Please note: the Key User Rule Editor is a Key User tool only and must never be used by a PDI Development User!
If you have a Business User you have access to the Key User Tool which will be enabled via the Adaption Mode in the C4C system where you can enhance the UI with variety of functions -> Adding ext. fields, adding rules, etc.. The Key User Rule Editor should be used by Business Users only, using Adaptation Mode in C4C. Login to the UI, click Adapt > Edit Master Layout.
If you have a PDI User you an use the UI Designer which can be accessed from the Cloud Application Studio. In here you can open the corresponding UI screen and then use the Extensibility Explorer to enhance the UI screen.
How to use rule editor - https://youtu.be/HWLz9mgbN2M
How to create a custom rule in opportunity - https://youtu.be/IVwcREzCBsE
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