13. When to use vouchers that top up a cell phone?

Please limit the use of these vouchers as much as possible to times when:

1. Sending direct top up by the standard command does not go through.

2. You receive the message Product ddtu is currently inactive for sale.

3. You receive the message Product ldtu is currently inactive for sale.

Please note that the products are not connected to each other, that is ddtu may not be going through or inactive while ldtu is working and vice versa.