It is possible to find a difference between the amount you paid and the amount of Mechanium you received. Don't panic, you have received the right amount of Mechanium.
We take the price of the cryptocurrency you are using at the time of the transaction validation.
Thus, the market may fluctuate.
We can see below the variation of the USDT over a few minutes, which can then impact on large amounts a difference of a dozen Mechanium.
This discrepancy is absolutely normal and has always existed in the cryptocurrency world.
You did receive at time t the exact number of Mechanium at the current rate of the cryptocurrency you used to pay.
To give an example, usdt can go to $1 or $1.0010 or $0.99
So if you take $10,000 worth of Mechanium and the Mechanium is at $0.284 per unit, you will get 35,211 Mechaniums if the USDT = $1
But if the USDT = $0.99 your $10,000 is worth $9990. So you will get 35176 Mechaniums.
The price is indeed the price of the cryptocurrency at the moment T, which can vary between the moment you enter the transaction and the moment the payment is made.