When using the Storefront Branded default theme, some Sitecore Forms functionality, like validation, and so on, might work incorrectly, and therefore prevent forms from submission. The following error might be displayed on the page:
SyntaxError: Unexpected end of JSON input
This happens due to the fact that Sitecore Forms and Sitecore Experience Commerce JavaScript files conflict.
To resolve the issue, download and install the hotfix compatible with the affected product version:
Be aware that the hotfix was built for a specific Sitecore XC version, and must not be installed on other Sitecore XC versions or in combination with other hotfixes. In case any other hotfixes have already been installed on a certain Sitecore XC instance, send a request for a compatibility check to Sitecore Support.
Note that the ZIP file contents need to be extracted to locate installation instructions and related files inside. The hotfixes must be installed on a CM instance and then synced with other instances using standard development practices.