The reason is that these watches are using android 7.1.1 without certification from Google.
Therefore no security patches are applied and the device is going to show up in the play store as not certified
Not because the watch makers have a problem - the problem is Google refuses to certify any kind of watch that does not use WearOS.
So even though there is no root and the watch is secure - it will never meet the requirements of that Sky app or Google Pay or any app that requires security.
When (and if) the next generation of Android watches comes and if Google will work with it - things might improve.
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