You are sharing a web feature layer or a web scene layer with an associated web feature layer. The feature layer contains data that is z-aware but no default z-value is defined. This means that you cannot edit the web layer in Map Viewer or in other clients that do not allow you to set z-values. (You can edit the web layer in clients such as ArcGIS AllSource that allow you to set z-values.)
Solution
Set a default z-value for features.
Hover over the analyzer message. Click the Options button 
that appears and click Show Feature Properties. In the Share As Web Layer pane, on the Configuration tab, check the Apply default to features with z-values check box and type a default value to use when features are inserted or updated.
More information
Setting a default z-value ensures that features can be inserted or updated in clients that do not support setting a z-value.
For more information, see Analyze your GIS resource.