My guess is that it is related to
I think Adalo sticks everything to the top of the screen, so if your screen is longer than the editor screen it will cause this. If you scroll a couple of messages lower in the link above @dilon_perera gives a pretty nice workaround for the problem. However, this only works if the component is full screen.
So, if your better webview component is the entire screen, and the pay button is centered in the webview, the trick Dilon shows should fix the issue (make the screen bigger than a normal screen so Adalo will scale it properly). If you have centered the better webview in the center of the screen so it perfectly shows the pay in the center then this trick will not work.
A very technical solution could be, rather than using a url for the webview, use HTML along side the trick Dilon explains, and it should work. Something like
<div style="width: 100%; height: 100%; display: grid; align-content: center; justify-content: center">
<iframe src="YOUR_PAYMENT_LINK"></iframe>
</div>
it might take a little adjusting.
If your webview is not the size of the screen, and Dilons trick does not work. It will probably be better to ship as is with it off-center. I do not think you will lose customers over it. Accept it as a limitation to using a No-Code platform.