In this blog, i will show how to filter lookup field based on the another lookup field in dynamics 365 without using any JavaScript code.
Open your main form through make.powerapps.com
Next select the field you wants to filter and in the right side scroll down and then we can see filter option and click on the filter arrow and next click on the checkbox.
Next in the first dropdown choose the parent lookup field here its Existing case(Customer field) and in the next dropdown choose the correct relationship and publish the form.
Next test and see its working
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