You cannot punish the performer after the state contract has been terminated by agreement of the parties
The parties signed a contract for the provision of transport services. They were provided at the request of the customer. The obligations were partially fulfilled, the contract was terminated by agreement of the parties. There were no complaints, as indicated in the supplementary agreement.
Later, the customer demanded that the contractor pay a penalty for the delay: several applications were fulfilled with a delay. He refused.
The courts of the first two instances supported the executor. So, they indicated that the obligations under the contract were fulfilled. This is confirmed, in particular, by payment documents and an additional agreement.
The cassation agreed and added the following:
the desire to terminate the contract was mutual;
termination of the contract was not caused by improper performance of obligations;
at the time of the conclusion of the additional agreement there were no claims;
The terms for the provision of services for the disputed applications were approved by phone, which is why it is impossible to establish a delay.
The Supreme Court took a similar position and did not review the case.
Note that in law enforcement practice there is a case when the courts refused to collect a fine for deficiencies identified after the signing of acceptance documents.
Document: Definition of the Armed Forces of the Russian Federation of 08.21.2020 N 309-ES20-10802