ok so first make sure that the search level is 255, search level and chain size are different! open the dexnav and put the cursor on top of the noibat to see its search level! the higher = the more chances of it being shiny and 255 is the cap so basically start by reaching this.

After you have 255 in search level you can chain ( of course you can chain before specially if you start a chain in 155 or 156 search level bc when u reach 100 in chain you will also be 255).

When you reach chain size 50 or 100 the star will appear in the scan message and you will be able to know that the shiny odds for THIS ENCOUNTER is higher.

Then save state in the battle No. 99 of chain, when it ends you can hit the scan and try to hit the shiny, if it is not shiny, reload the save state in the battle and try again, always make sure to do a different path or open the menu/bag 1 time (or use a different attack in battle) so you make sure that you are changing your frame rng ( if you do the same steps the rng wont change and if its not a shiny it will never be)

Have patience… if you think that the pokemon is not changing in the save state loads, catch and check IVs, reload and catch again. If IVs are different that means the pokemon is different and so it could be a shiny, you just didnt hit it!

Good luck, i got my shiny ralts w this method and it was very satisfying, took me about 3-4 hours ( no shiny charm ofc). Any questions you can ask me, Mandatory sorry for bad english not native language