A User channel can not be accessed by python api

I want to make a user channel in a stack and edit it by Python API.

Making the user channel will succeed but I can't access it.

How do I access the user channels.

from substance_painter import textureset
ChannelType = textureset.ChannelType
ChannelFormat = textureset.ChannelFormat
for tex_set in textureset.all_texture_sets():
    for stack in tex_set.all_stacks():
        if not stack.has_channel(ChannelType.User14):
            stack.add_channel(*channel_param)
        print(stack.all_channels())
# [Python] There is no channel 'user14' in the texture set.