I am trying to create an ECA workflow to assign a custom role on user registration based on drop down field selection.

User selects Value 1 from Custom_Field on registration form, clicks Register, Custom_Role gets assigned.

Can someone point me to what the ECA workflow should look like, either Classic or BPMN version?

ChatGPT has provided dozens of suggestions, none have worked.

I could have built this with Rules module without any help but ECA has completely lost me.