spfx extensions – CORS and SP2019 on prem dev

I’m again trying my hands on some SPFx development on code downloaded from GitHub. As we are behind firewalls and they won’t open anything I have to use a local CDN for all my manifest files and what not.
Now some of the small devs i have done work fine but some of them i run into the CORS issue with the error below

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Now one of the dev’s that i played with i did get to works with the below code as i did get some great help from this community

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However when i try to do this on this latest dev below I can’t get it to work. Below is the full ts file and i just tried to enter the same code.

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I’m a inhouse guy who got thrown into this because I like to tinker but I’m now in way over my head. If anyone has some time to help it would be great. The code that I started with for CORS is here