locking the plc using programing in S7-300 simatic manager

Dear all can anyone suggest the method to lock the plc or to stop the machine

As the customer is not doing the payment of the work

please suggest me some smart techniques

The only way I know of to get the customer paying is to let the lawdo it's work, in other words: go to an attorney and let him/her start a case. All other methods may fire back at you in the end.

For bigger projects or machines, customers must provide a letter of credit before any work or shipping of parts will be done.
Typically payments are split up in stages, 5% for preproject, 40% for start of design and purchase of parts, 40% before shipping, the rest upon acceptance of the machine. The split may be different, this is just an example. The problem is of course how to get the last payment. In the worst case it may come down to legal actions.