If you're using variants in the Kaching Bundles app, make sure to enable the Enhanced Ajax API Compatibility setting in UpCart. You can find it here:

Cart Editor > Settings > Advanced Settings > Enhanced Ajax API Compatibility:

If you are still experiencing issues between UpCart and Kaching offers, additional work by the Kaching app developers may need to be done. In these cases, please reach out to the Kaching Support via their documentation page.