Currently, the client has nothing past due, and they are able to meet the entire obligation on time. You could use "they're" instead of "they are" to sound more informal if you like. You could also specify "Currently, the client has no ____ past due," example: "Currently, the client has no bills past due, and they're able to meet the entire obligation on time."

currently no overdue payment

What do you mean by 'past due'? Do you mean currently overdue payments? or that they have had overdue payments in the past?