fix: type

Author: chedieck

react/lib/util/api-client.ts

@@ -93,7 +93,7 @@ export const createPayment = async (
   amount: string | number | undefined,
   address: string,
   rootUrl = config.apiBaseUrl,
-): Promise<string> => {
+): Promise<string | undefined> => {
   const { data, status } = await axios.post(
     `${rootUrl}/api/payments/paymentId`,
     { amount, address }