[Abagail]

You'd need to use the paypal API. Additionally, I don't know what kind of user-saving system you use:
I am guessing that you are using MySQL so basically this is a snippet from my gamemode(Xenon Gaming):

pawn Код:

stock DoesAccountExist(szName[])
{
     new query[500];
     mysql_format(MySQLCon, query, sizeof(query), "SELECT * FROM `players` WHERE `user` = '%e' LIMIT 1", szName);
     mysql_tquery(MySQLCon, query, "", "");
     new rows, fields;
     cache_get_data(rows, fields, MySQLCon);
     if(rows)
     {
        return 0;
     }
    else
    {
        return 1;
    }
}

Basically you need to check if a row is exists. And as for the paypal API, just ****** it, and ****** will assist you with that.