Most services require an Access Token. To get one, you first need to get your seller's account credentials.
To do it, go to https://www.mercadopago.com/:siteId/account/credentials
(where :siteId is your account’s country id) and log in. You can now access your client_id and client_secret.
mla - Argentina
mlb - Brazil
mlv - Venezuela
mlc - Chile
mlm - Mexico
mco - Colombia
mlu - Uruguay
Example (Uruguay): https://www.mercadopago.com/mlu/account/credentials
The credentials to be used depends on the kind of interaction that you are going to implement. This could be Basic ou Custom Checkout. Once you get your credentials, you must setup the SDK to use them.
In the SDK in GeneXus, find the “GetCredentials” procedure and set &Client_id and &Client_secret with your credentials from the "Basic Checkout" tab.
To get your token, call the procedure GetAccessToken(), which returns an AccessTokenSDT with the token's information. Keep in mind that for Basic Checkout this token is valid for 6 hours, after which it must be renewed.
Note: In Sample, there is a procedure (GetCurrentToken()) that calls ObtainAccessToken(), which renews the Access Token automatically if necessary, every time it's needed, saves it in your local BD and returns a valid token.
See MercadoPago Custom Checkout