My component where I am passing validate prop ->>>>
<div className="label-input-container activity-reason-dropdown">
<Dropdown
dataAutomationId="identification-activity-reason"
name="identificationActivityReason"
label={<Translate id={isFromParameter ? 'updateParameter.updateReason' : 'commonComponentsLabels.activityReason'} />}
values={options}
disablePortal
disableClearable
mandatory
**validate={(value: any) => {
val(value);
}}**
customDropdownClass="activity-dropdown-heigh-issue"
placeholder="Select Reason"
/>
</div>
validator intermediate function ->>>>
const val = (value: any) => requiredActivityReason(value, customProp);
actual validating function ->>>>
export const requiredActivityReason = (inputValue: any, customProp: any) => ((inputValue || typeof inputValue === 'number') ? undefined : 'Please select activity reason');