It is an independent feature. How does you channel policy look alike?
E.g you can create channel policy which says:

method build && bool target && match target-for-using-channel-xy :: use xy

Such policy would be triggered independently of srpm/git input as it doesn't care about the source.

Hello, I have set up such a strategy in "hub.cnf"
method build && bool target && match test :: use kojiadmin
Submission method: channel is a custom channel name, elzi is a tag name
koji call build timedatex-0.5-1.test.src.rpm elzi channel=test
But it still reports the same error as before. Why didn't Koji import the source code package instead of searching for it from the Kojifiles path

Or I want to implement using a local source code package to specify a channel for submission, but now I can only submit using the git+http link method after specifying the channel

1) Ouch, I've missed a keyword in the example - there is missing what should be matched.

method build && bool target && match target target-for-using-channel-xy :: use xy

2) "kojiadmin" in your policy looks suspicious as an user name. It should be channel name, so probably "test" in your case

3) you can't build via API as easily (some other API call must be made to upload SRPM first). OTOH, I'm not sure why are you doing that. Simple "koji build " will upload the srpm and use channel from that policy.

Hello, after making the following modifications in hub.cnf, the policy has taken effect and met my expectations. However, after multiple rounds of debugging, I am not very familiar with the syntax. Do you have detailed documentation about the policy? Koji's official documentation is only a rough introduction.
hub.conf
channel =
has req_channel :: req
is_child_task :: parent
match target mytag && all :: use test

https://docs.pagure.org/koji/defining_hub_policies/ is the basic documentation. It would be worth of expanding it but that is what we have.
In your policy last line has rendundant part '&& all' - it will be always true, so ony match target mytag is enough. Anyway, I would expand it to bool target && match target mytag :: use test as not every task (e.g. createrepo) has the target attribute, so it could sometimes fail on missing field.

Okay, thank you very much for your answers and suggestions.
I have a request. The most basic tool I use in my work is Koji, so I will join one of your groups or organizations. I want to learn more quickly and deeply, and I am willing to contribute to it to the best of my ability.

This issue has been migrated to Fedora Forge:
https://forge.fedoraproject.org/koji/koji/issues/4143

Please continue any further discussion there.