Generally when Excel code works in debug mode or release mode on a developer's box then fails on a client's box means either the client does not have Excel installed or does not have the correct version of Excel.
The best solution is not to use Excel automation, instead use an Excel library which is not dependent on Excel being installed. Two of many free libraries
And there are plenty of paid for libraries such as
And there is always the option to skip libraries and code what those libraries do yourself