What is the best way to offer paid support after the project is completed?

Question

Freelance

The project is ready. TOR completed. How to offer a client paid support for a project created for him.
In particular, now the question is about an online store on a self-written engine.
But in general, it’s interesting how best to present it so that it’s not just hosting services with a small markup from the average market price, but also, for example, round-the-clock support, updates, and some other services.
The client believes that he does not need promotion services now, but perhaps something else can be offered.
It is also interesting how to justify the need to order support, since I think the question may arise why it is needed if it is claimed that the project is well done and no bugs were found.

Answer 1

is still comparable

• if you do not buy a support package, a call on demand will cost N$/hour, but not less than X$
  
• if you buy X hours of technical support it will cost Y$, save M$ of money + response speed will be higher than for a one-time service
  

Answer 2

Make sure nothing will work on its own. And if not maintained on a regular basis, technical debt will accumulate.

Answer 3

and so that, for example, round-the-clock support, the delivery of updates, and some other services.

Only under a contract with an indication of the entire range of services .
The client believes it is true: a project that is executed correctly does not need TP during the year.
Such a project only needs to be promoted and respond quickly to new IP requirements (new tags, new structure file formats, etc.).

Answer 4

Take a BM course on packaging.