All of the involved parties should fix the problem on their own. Any single one of them fixing the issue won't prevent it from popping up again, since you can substitute or circumvent the fixed layer.
Signal should handle this case explicitly in the app, since it's a common frustration for their own users when typing dots, commas and parenthesis.
Android should maybe fix the library, but at the very least fix the documentation to mention that it is not intended to be used in context of prose. Android fixing their library is the least useful of all possible fixes, since it won't propagate to users of Android in any meaningful way for a decade.
The Virgin web team should see that there's elevated 404's, and configure their system to ignore trailing full-stops.
A company the size of Virgin probably already has a process to review marketing messages, but it's likely to be someone eyeballing it, and they should fix it to catch this automatically. They probably already use a marketing automation and scheduling system, that could fix it by verifying the links before pushing.