I'm sorry if you're trying to advertise here, but this won't work
I'd recommend posting on your account, and putting it on your bio
If you've tried that already, then probably try advertising in popular posts. Just don't be too annoying, you can just comment once
Also maybe change up the way you say to subscribe to your channel, use some pizzaz. Make it pop out more
Like
Hey, Can you pretty please sub to our channel?
(link)
Have a good day!!
Something like that, you're probs not gonna read this but might as well