What to do if by mistake I’ve bought a Standard account instead of Direct Connection?

If you pay with the command /powerup, then you buy a standard account. To buy Direct Connection you should use the command /poweruppro 12. Direct connection is a different service and is more expensive than a standard account. Please see here the comparison.
If you made this mistake, don’t worry. Just pay the missing amount with the command /poweruppro and let the bot’s admin know, we will transfer your first payment to Direct Connection.