fix error message of donation for conservation form

public/static/locales/en/manageProjects.json

@@ -29,6 +29,7 @@
   "treeCostValidaitonRequired": "Please enter cost per tree",
   "treeCostValidationInvalid": "Please enter valid cost per tree",
   "treeCostValidation": "Cost per tree should be more than €0 or lesser than €100",
+  "conservationCostValidation": "Cost per m2 should be more than €0 or lesser than €100",
   "projectLocation": "Project Location",
   "visitorAssistanceLabel": "I will provide lodging, site access and local transport if a reviewer is sent by Plant-for-the-Planet.",
   "publishProject": "Publish Project",

src/features/user/ManageProjects/components/BasicDetails.tsx

@@ -765,7 +765,12 @@ export default function BasicDetails({
                   <span className={styles.formErrors}>
                     {errors.unitCost.message
                       ? errors.unitCost.message
-                      : t('manageProjects:treeCostValidation')}
+                      : t(
+                          router.query.purpose === 'trees' ||
+                            projectDetails.purpose === 'trees'
+                            ? 'manageProjects:treeCostValidation'
+                            : 'manageProjects:conservationCostValidation'
+                        )}
                   </span>
                 )}
               </div>