I'm working in SandBox mode
I do not know if something happens with MercadoPago or it's me, but the icons of some means of payment do not appear. These icons vary. Sometimes all appear well and sometimes none appears.
And also when I pay by credit card, I see the following URL in Networks of Google Chrome:
Is Sandbox mode working well?
Good, I had the same problem and note that the v1 / payment_methods endpoint comes and goes constantly when you use the test credentials.
Notice that using the production credentials to bring the payment_methods you will not have problems (If your app is not approved it does not matter, for the payment_methods you can use the production credentials).
For those who are having the problem of No 'Access-Control-Allow-Origin', I also went crazy with this. The MercadoPago API, although it says that it should, does not send the Access Control header, so Chrome (and other browsers) block the connection.
You can download the Access-Control-Allow-Origin extension from the Chrome store to test the integration or use link as proxy for your requests.
Essentially if you want to make a request to api.mercadopago.com make the request to " link ". If you visit the proxy link find the instructions to host your own proxy, which I recommend for reasons of security and stability of their platforms.
I hope I have helped you!
Greetings!