I am working to use AWS codepipeline but unfortunately the url used in the external/catch submodule needs to have .git appended to the url as AWS has troubles sometimes with submodule urls that do not end in .git . Following link has some explanation
[https://stackoverflow.com/questions/53785769/aws-codebuild-error-on-download-source-client-error-repository-not-found-for-p|url]

file: realm-object-store/.gitmodules

From:

[submodule "external/catch"]
path = external/catch
url = https://github.com/catchorg/Catch2

To

[submodule "external/catch"]
path = external/catch
url = https://github.com/catchorg/Catch2.git