It is all about patience and timimg
Is the spawning tank in a quiet area of your house? Sometimes if there are people moving about a lot of the day it can be a distraction.
All i can advise is -
Male in spawning tank first for a week whilst being fed high protein foods.
Dont have too much stuff in the tank - just heater, sponge filter, maybe a plant, and bubblewrap or polystyrene.
Get the temp in the tank up to about 30c and only 6 inches of water maximum.
Keep female seperate from others so you can feed her up too for approx 2 weeks.
Then put her in the chimney and keep feeding both high protein foods.
After about 2-5 days she should be looking nice and fat. But normally 2 days is adequate.
She may or may not be showing vertical bars.
He should be taking interest in her and have at least attempted to build a nest. Dont worry if the nest is small.
Release her for a couple of hours, and then put her back in the chimney overnight.
Release her again in the morning and wait, and wait and wait.
She may get nipped and receive damaged fins, but as long as its not too bad leave them to it.
You can put her back in the chimney each night.
Remember to keep feeding good food during this time.
Once they start spawning, it should take about 2-6 hours. Dont be tempted to remove her too early. You will know when they have finished because the female will hide! The male will be standing guard and will chase her away very quickly.
Remove her and keep her seperate from other fish for at least 2 weeks so she can recover with good high protein food.
Then just leave the male to do his stuff. Remember to leave a light on overnight.
After about 3-5 days most of the fry should have hatched and be free swimming. You may see him swimming around collecting them and taking them back to the nest. Once they are mostly free swimming you can remove the male.
However, sometimes they are just not compatible and there is very little you can do.