<font face="Arial, Verdana">You do not add it, you change the value. Both are in both variant selectable. Check Configuration.h</font>
<font face="Arial, Verdana">#define FEATURE_AUTOLEVEL 1</font>
<font face="Arial, Verdana">#define FEATURE_Z_PROBE 1
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<font face="Arial, Verdana">If you add it it might be overriden by already present value.</font>