Features cannot be added or edited in the ArcGIS Online map viewer when an empty Z-enabled feature class is published from ArcGIS Pro as 'Copy all data: Editable'.
To allow editing on the service layer, follow the steps below.1. From the Admin API of the service, click UpdateDefinition. 2. Change the enableZDefault value from 'false' to 'true'. 3. Change the lastEditDate value to 'null'.4. Click Update Layer Definition.