I have applied filed validation in system.xml file it is working for other fields but not applying on Dynamic fields.
Here is my Dynamic Field:
<field id="add_item" translate="label" sortOrder="15" showInDefault="0" showInWebsite="1" showInStore="0">
<label>Set Dropdown Prices</label>
<frontend_model>Vendor\Module\Block\Adminhtml\Menu\Field\AdditionalItem</frontend_model>
<backend_model>Vendor\Module\Block\Adminhtml\Menu\Config\Backend\AdditionalItem</backend_model>
<validate>validate-digits</validate>
</field>
Update
Here is my column in Frontend Model:
$this->addColumn(
'productcost',
[
'label' => __('Voucher Cost'),
'size' => '150px',
'class' => 'required-entry'
]
);