The calculated price of tarif low is not correct.
@woskam Hello and welcome to the community
can you please give us more information so we can help you 
The value is not retroactive. If you added the price 10 minutes ago, but your kWh was added 5 hours ago, the values between 5 hours ago and 10 minutes ago are not in the calculation. Only the last 10 minutes are calculated because the previous 4 hours and 50 minutes do not have an associated price.
The other prices are correct for over a month, so???
And? I don’t think you understand. The calculation takes each item in your database and multiplies it against the price at that moment in time. If the data has no matching price, it will not add that portion to the calculation.
E.g.
| time | state | price |
|---|---|---|
| 8:00 | 1kw | - |
| 8:15 | 1kw | - |
| 8:30 | 1kw | - |
| 8:45 | 1kw | $1 |
| 9:00 | 1kw | $1 |
| total | 5kWh | $2 |
It does not multiply the total result against the price. It multiplies the value in the database by the price in the database, then adds them up. So if you added the price late, your cost will not match the total kWh because it doesn’t have the price for some of the data.