@PK The PR has been accepted so should show up in the nightly build. I'm not 100% sure it will fix the issue but it wont do any harm.
Can you supply an INDI log that shows where it fails and/or describe what fails?
Meantime I'm going over the Nexdome firmware code itself. Based on the documentation the protocol change going to 4.0.0 is minimal but the code may show something else.
Also note the first bullet in the release note:

Breaking Change
This release is a breaking change for two reasons.
- The memory layout of settings has changed, so on upgrading all settings will revert to factory defaults.
- Some response and notification messages have changed slightly to give more consistent formatting and fix issues.
Developers who access the firmware directly will need to review the Firmware Protocol document.
I made a change based on the second bullet but in fact, as far as I can tell, the formatting did not change at all. They just added a new command and response.

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