I don't know how much this plugin is maintained, but I'm happy to contribute to development to resolve some issues.
I have Gravity Forms set up to create a blog post and submit the form to Infusionsoft. The text area field used to populate the blog post content throws the following error on form submission whenever someone copies and pastes ANY text content from a document (such as Word, Textedit, a website, etc):
Fatal error: Uncaught Failed to parse XML-RPC request: Invalid byte 1 of 1-byte UTF-8 sequence. thrown in /home/angela/public_html/directory/wp-content/plugins/infusionsoft/Infusionsoft/App.php on line 51
When using an Infusionsoft form directly from the Infusionsoft site, this error does not occur, so it is only when using Gravity Forms with the Infusionsoft plugin that there is a problem. Also, Gravity Forms alone does not throw this error. It is particular to your plugin. Here is some information I found on the IS site, though not sure if it is helpful: