Update API Reference

API-Reference.md

@@ -79,6 +79,39 @@ Only one may be used, as no conflict is permitted in same request
 ]
 ```
 
+#### `POST /department/activity`
+ 
+Setting activity by identifier.
+ 
+**Request bodys examples:** 
+
+Only one may be used, as no conflict is permitted in same request
+
+```json
+[
+  { 
+  "code": "ENG",
+  "active": false
+},
+]
+```
+```json
+[
+  { 
+  "code": "Marketing",
+  "active": true
+},
+]
+```
+```json
+[
+  { 
+  "cost_center": "CC-1100",
+   "active": true
+  },
+]
+```
+ 
 
 
 #### `DELETE /departments/delete`