Mobile : The UI object is invalid. make sure the target application is open

The error message is telling you exactly what is wrong. It couldn’t find a suitable selector for that area. The supported selectors are starting with mbl, html or webctrl. If you think that, that area is part of the webpage then look in the visual tree and see if you can find it.

If you can find an area that the position of the button is relative to: meaning that it will stay at the same offset, then you can still click that by using click with offset.