Someone has created an App for my website (converted my website to an android and iOS app), but now the call buttons and Anchor tags are not working on the App, however they do not have any problem when my website open in browsers like Google chrome or fire fox browsers? could someone please tell me where is the issue?

<a href="tel:+964__CUSTOMER_TEL__" style="width:35%; float: right; background:#ff9933">
    <i class='fas fa-phone' style='font-size:16px'></i>
    __CUSTOMER_TEL__
</a>