Reinstalling MacOS Catalina giving error messages

I wanted to repartition my brand new macbook pro 2019 model that came with Mac OS Catalina 10.15.1 and now after wiping the full disk I am a bit stuck.

As there is no option in the disk utility window to repartition existing APFS disks to differrent sizes I had no other choice but to reinstall the OS after wiping the drive.

Here are the steps I went through.

1. Boot the OS into recovery mode before wiping the host OS, I then changed the startup security settings to Medium security to allow signed operating systems to run, allow booting from external media.

2. Downloaded the latest Catalina OS 10.15.3 from the app store and then uses the -createinstallmedia command to create one external drive into a bootable Catalina Installer.

3. I ran the installer off the external drive which needed to connect to the Apple servers initially for validation, then after that process finished, an error occurred stating that "Mac OS could not be installed on your computer, an error occurred installing MacOS to use Apple Diagnostics to check your mac hardware, shut down, press the power button and immediately hold the 'D' Key until diagnostics begin. Quit the installer to restart your computer and try again"

4. Then I went for the internet recovery option for booting. After booting into internet recovery, I went to the disk utility and once again formatted the internal drive to clear any previous installation partitions. I once again created the partitions with the sizes I wanted and ran the installer. After the installer completed I received an error message "macOS couldn't be installed on your computer, Couldn't complete copy. : (-69512) Quit the installer to restart the computer and try again"

That is the point where I am stuck and I could use some assitance. I am unable to load the OS on this macbook pro again.

I was not able to run Diagnostic mode as it asked. When I pressed diagnostic mode the computer stays stuck on a black screen for over ten minutes and does nothing. Also, with the internet recovery mode as it is an 8GB download my organization network is quite slow, so I tried from my mobile hotspot and it would take over 8 hrs to get to the error message, then I attempted on my organization network without any proxies/network blocking and still the same result.

Could there be some timeout issue with downloading/verification happening on the network?

Should I have instead put the security settings to allow any installer instead of Medium? At this point the recovery mode partition is gone after formatting the drive, so I cannot change the settings once again.