When your channel about link telegram viral gains 3 thousand subscribers or more, you can increase this figure by an average of the same number with the help of mutual PR with other large channels. This is from each partner and absolutely no cash costs, unlike advertising.
You advertise another channel, and this channel advertises yours. The mutual benefit is that both channels exchange subscribers. Of course, everyone strives for mutual PR with a channel that is approximately the same in volume.
At the very beginning, there is no point in mutual PR. And other large channels are not interested in cooperation with newcomers with a small base, from which it will not be possible to get a decent influx of subscribers.
These are free methods. It is also possible to purchase ads in other Telegram channels.