It takes a local ‘system’ change to trigger the pay out. Completing a level constitutes such a change. Try some of these: A fun blast from the past! to see if you can get it to pay…don’t use them all up frivolously 
Keep in mind, the formula is 20 x ^ .4, where x = the number of sims completed. I got to 1.65M and received over 6000 gems. I had 3 farms running 24x7 and it took me about a week or so.
Also, if you have limited bandwidth or are on a data plan, be very careful of data usage…if you are running multiple farms, the data usage racks up pretty quickly. (Remember, a gem farm is 9 sessions running in tandem.)