Worried about participant recruitment


I'm a few weeks into recruiting participants for my first study, and I'm not getting the kind of engagement I was expecting. I've shared the link to my survey on social media, but I seem to only get 1 or 2 responses for every 4 posts I make. My participant group is quite niche (so not all adults over 18 or something like that), but I did another study a few years ago using the same group, and got a relatively good turnout in the same time period. I'm wondering if screen/online fatigue is playing a role this time - I know a lot of research has had to go online, so a lot of forums etc. are no longer accepting survey promotion posts.

I'm planning to approach some organisations direct to see if they are willing to help me with recruitment, but what I was wondering is: what would happen if I can't recruit the numbers required? Has anyone experienced this before?