For some reason this did not come up when I hit view new posts yesterday.
Articles on this are in the works. Everyone has a different approach of course.
The nests probabaly disintergrated because there wasn't enough stickiness/mankiness in the water. Do you have any live plants? Are the tanks covered? The tank needs a lid to keep the humidity in or the bubbles will almost always burst.
Are you planning to spawn in a 5L tank?? That is far too small. I would use a 10L tank, minimum. Preferably 20L.
It needs to be cycled or ammonia will kill your fry. You will need (IMO) a small sponge filter in one corner. Have a valve so you can turn the bubbles down to 'barely bubbling".
You will need some sort of nesting material or 9 times out of 10 the nest will disintergrate. I use bubblewrap or yellow plastic.
You will need to have microworm or vinegar eel cultures ready to feed the fry. You should also, IMO, practice hatching brine shrimp so you can feed newly hatched bbs to the fry once they are big enough (ie once they are 3 - 5 days old).
IMO the male should have the run of the (cycled) tank for a week before you add the female. This gets him territorial and full of testosterone. Show him another male or mirror during that time if you want to get him really fired up.
Feed the male and female lots of high protein food that week to get them conditioned for breeding. Live Blackworms and mozzie wrigglers are popular for this. Grindal worms are also excellent but not commonly available.
After the week add the female INSIDE a clear container (eg coke bottle with the bottom cut off) so he can see her but can't get to her. Don't release her if it looks like she is petrified of him or like she is trying to kill him (as opposed to flirting with him). If she is flaring head down and with dark bars (if she is a red or blue fish) they are good signs. She should look fat with eggs. She may even start dropping eggs if she is really ready.
Be prepared for them to beat the crap out of each other once you release the female, and possibly for one or both to die. Also be prepared for them not to spawn for several days. Give them hiding places (not a terracotta pot they can get wedged in the hole of, though).
Lastly, most LFS bettas are getting on in age and may not be the best candidates for spawning. However many people have had prolific results from LFS VTs so this is not a "rule" just a comment.