Hi @サンデャ 管理者
I understand that you would like to know the custom rule created in synchronization rule editor is working fine or if there are any errors.
You can validate the newly added sync rule by using the preview feature, without running the full sync cycle for more information refer Validate sync rule. You can also refer How to identify modified default rules. I hope this information helps! please Feel free to ask any questions you may have. Thanks,Akhilesh. Please "Accept the answer" if the information helped you. This will help us and others in the community as well.