Would an ATM memo post or POS authorization be considered an "error" under Regulation E?

For example, a gas station may allow an authorization to be less than or more than the acutal purchase. The POS authorization is approved for $20, but the acutal transaction amount is $10. If a consumer can view their POS authorizations and noticed a discrepency, can the consumer invoke a Reg E "error" notice and would the financial institution be obligated to research?

What if the financial institution held the authorization amount until the acutal purchase posted to the account (2-3 days later)?

The same question for ATM memo posts. Can we tell the consumer to wait until the transaction posts before invoking a Reg E "error" notice if there was a discrepency between the memo post and the acutal amount the consumer received?

There is no error until and transaction posts to their account. That is the danger of allowing customer to access memo posting - they don't understand it.

Another scenario. Financial institution holds the $20 POS authorization for 2 days until the acutal $10 purchase posts to the account. The customer only has $20 in their account. A $10 check tries to clear the account, but the $20 POS authorization is holding the funds until the acutal purchase posts. Would this invoke a Reg E "error" because the POS authorization caused a fee for insufficient funds and because there was a discrepency between the authorization and acutal purchase transaction?

Well, here you have a problem, because the real course of action from the consumer would be to sue you for wrongful dishonor, not a Reg E violation. Again, the transaction has to post to the account for Reg E to kick in..

Do you have any regulatory language indicating that the Regulation E error rules do not kick in until a transaction posts? In the above scenario, for all practical purposes, the transaction occurred since the customer does not have access to the funds.

It only occurred since you have, from an operational perspective, posted the memo amount to their account which inturn has reduced their availability. Those actions by you are not governed by Reg E and should be looked at under funds availablity and the UCC.