it working now, but it hard to make it work.
step 1 n 5 is very important before go to step 6.
u cannot connect with group/channel is u not login telegram at https://web.telegram.org.
after u get the api and add bot as admin to group/channel, u must type a new message on that group/channel, then immediately add telegram api on stackpost. if u delay to add it, stackpost cannot detect group/channel.
also stackpost not detect all group/channel list that joined by ur bot, it only detect which group/channel that u send new message. but sometimes it can detect all.
also old bot sometimes cannot detect their api, u must create new bot to get api. i not sure why it work like that. hope it can improve. thanks