Can't find variable: fetch

I have a Shopify store API, implemented in aspx and c# but in some navigators return this error:

ReferenceError: Can't find variable: fetch

on line: index.umd.minjs:25:7483

CDN: <script src-"sdks.shopifycdn.com/js-buy-sdk/v2/latest/index.umd.min.js"></script>