Your manager promised us...

Very often we hear such words from our customer.

And it's good if the manager, who hasn't been working for six months, promised to replace the favikon for free, instead of completely changing the logic of the calculator and "we will change the design for you even after the development. Of course, it is possible, having taken a hard breath, to begin to carry out "agreements",
or with foam at the mouth to enter into a dispute with the client, losing their nerves and customer loyalty. How to make a straw in advance?

Minutes of meetings. At the end of the meeting with the customer all agreements must be recorded in writing, and then receive confirmation from the customer that this is what you have agreed. If you missed something, the customer will correct you himself. The same approach is applied to telephone conversations and communication in messengers (it is about meetings and agreements, not about every call).

And it does not matter if such protocols are mentioned in the contract - it still has effect.