When written, the sentence is not well-formed. When heard in your linked video, it is slightly clearer (but maybe because I have worked in software development, which is the subject of the video).
However, it is still a very awkward construction, and you shouldn't use it as an example of good English.
In the video, the speaker is describing how to implement communications with a third-party financial programming interface.
In the quoted part, he is effectively combining two statements:
He is warning that implementation mistakes are costly to rectify (e.g. because work needs to be redone, or because money incorrectly transferred is not easy to recover) — a mistake can be very pricey
He is providing an example of a common issue that can occur, which may cause your end-users to request the further support — chargebacks that[sic] are issues clients may have
It is ultimately a warning that writing code that works with money is hard, and that you need to be thorough (i.e. a "good developer") to make sure that you do it correctly.
For reference, the term, chargeback, is an industry term which is used to describe when a purchaser requests a refund for money they have paid via credit card. The credit card company often charges a fee to the retailer (not the purchaser), when the refund is processed.
Additionally, it is common for software developers to refer to the people who commission the developed work as the client, rather than the people using the developed work (often distinguished as the end-user).
There is also an awkward distinction in software, that a client can also be the piece of software that specifically invokes the methods of the third-party programming interface (where those methods are provided by the server).
I am fairly certain that, in the quoted part, the term client refers to the people/organisation who commissioned the implementation.