Before I start OCLP - macOS High Sierra says there are updates. It won't update native version - "An Error has occurred - forbidden(10403)"

So, reading through the guide and FAQ - it highly recommends not installing OCLP until I make native updates - there is an iTunes update but more importantly there is this update:

macOS High Sierra 10.13.6 Update - restart required
The macOS High Sierra 10.13.6 Update adds AirPlay 2 multi=room audio support for Tuens and improves the stability and security of your Mac. This update is recommended for all users

This iTunes 12.8.2 separate update - This update resolves an issue that may prevent iTunes from playing media to third-part AirPlay speakers. It also includes minor app and performance improvements.

I get the same error message on both attempts to update.

So, if I start OCLP will this cause problems down the road to update High Sierra up to Sequoia

Here is my info on version:
Model Name: iMac

Version 10.13 (17A405)

Model Identifier: iMac12,2

Processor Name: Intel Core i7

Processor Speed: 3.4 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 8 MB

Memory: 16 GB

Boot ROM Version: 87.0.0

SMC Version (system): 1.72f2

Serial Number (system): D25J60NQDHJW

Hardware UUID: 1057B9E6-9005-5890-9D7C-AFBE24AB8820

I appreciate any advice.
Cheers,
Jake