both of these errors are related to OPC, not square webPay.
as previously stated, something else is submitting the form; and that something else is OPC. you can look at this pull request here:
https://github.com/lat9/one_page_checkout/pull/410
and specifically line 424.
with regards to your grey screen zip code problem, that is addressed by the rest of the change in that pull request.
if you are running a version earlier than 2.5.0, you can look for that same section of code wherever it may reside and make the changes there.
if you can not read what is going on in that pull request, you can wait until the next release of OPC.
if your settings for OPC are to run minimized versions, turn that off until the next OPC release. or minimize the code yourself. i can provide no help for minimizing code.
best.
Bookmarks