How to test payments properly?

We have created a subscription based product and we are trying to test how it works. But we are getting errors and we are not sure whether its an issue with the plugin or configuration.
1. One of our users is testing this from asian country and he is getting an error without the mercadopago form:
“An error ocurred when proccessing your payment. Please try again or contact us for assistence.”
There is any ip/country banned in mercadopago??

Because I am testing from Argentina and I am getting the mercadopago payment form ok. However, I cant complete the payment and I am getting an error using the test creditcard numbers (the plugin has the sandbox test keys)
I enter the information (arventina visa 4509953566233704, APRO as name) and always shows:
“No podremos procesar tus pagos con esta tarjeta.”
What to do???

We are trying to test Subscription, how to test it??

BTW, I was reading here https://www.mercadopago.com.ar/developers/en/solutions/payments/basic-checkout/test/test-payments/
And it says that we must create two users… but… how do we use that???
Our developer says that paypal plugin works like that too, but you enter the users in the plugin configuracion

I have no idea what to do, and we are freezed trying to make a mercadopago implementation in a plugin… the documentation is obscure…

We are using wordpress 4.9.1 & WooCommerce MercadoPago 3.0.6