Jetpack 6.3.2 is now available for download. This point fix addresses a fatal bug affecting all sites using PHP 5.3 and below.
For those keeping track, Jetpack 6.3.1 technically exists, but was never officially released. 6.3.2 is the latest and recommended version.
For this point release, we fixed a compatibility issue with the Simple Payment Widget, released yesterday, with PHP versions 5.3 and below. Initially this widget caused fatal errors upon activation.
Thanks for your support!