I have joined more than 5 Facebook groups for online earning sake , and what I noticed is they advertise scam HYIP sites or Investment sites and post fake edited payment proofs. Also some people in the group share referral links of scam sites. Also there are set of "fake bitcoin mining managers" who message you in FB and ask if you are interested to invest in their scam mining programs. Immediately block them as well. It's better not to join any facebook groups related to online investment or earning sites.