fit(frontend): fix getOpenPaymentsUrl function (#3162)

Author: mkurapov

packages/frontend/app/shared/utils.ts

@@ -60,14 +60,18 @@ export function capitalize(str: string) {
 }
 
 export function getOpenPaymentsUrl() {
-  if (!process.env.OPEN_PAYMENTS_URL) {
-    throw new Error('Environment variable OPEN_PAYMENTS_URL is missing')
-  }
-
   if (typeof window === 'undefined') {
+    if (!process.env.OPEN_PAYMENTS_URL) {
+      throw new Error('Environment variable OPEN_PAYMENTS_URL is missing')
+    }
+
     return process.env.OPEN_PAYMENTS_URL
   }
 
+  if (!window.ENV.OPEN_PAYMENTS_URL) {
+    throw new Error('Environment variable OPEN_PAYMENTS_URL is missing')
+  }
+
   return window.ENV.OPEN_PAYMENTS_URL
 }