Hey RRobert.
Ok, I'll add this into our issue tracker and we will see it in our upcoming release.
For now to resolve this , find attached file and replace on below mentioned path. (default.php)
root\components\com_payplans\themes\wireframe\invoice\item\default.php
To apply this change for pdf invoice , find and replace the file on below mentioned path. (pdf_content.php)
root\components\com_payplans\themes\wireframe\invoice\pdf_content.php
Please take a look on this issue and let me know if any issue persist.
Thank you for understanding !