Hi @JNelson,
Could you please share a screenshot of your flow's configuration?
Do you use the "Send a customized email when a new SharePoint list item is added" built-in template to create your flow?
Further, could you please show a bit more about the error message?
I have created the flow with the "Send a customized email when a new SharePoint list item is added" built-in template of Microsoft Flow and update the content within "Send Email" action, I don't have the issue that you mentioned. My flow's configuration as below:
The flow works successfully as below:
In addition, you could consider take a try to create your flow from scratch, because, sometimes there is something wrong with the flow created by built-in templates of Microsoft Flow. Then check if the issue is solved.
More details about creating a flow from scratch, please check the following article:
Create a flow from scratch
Best regards,
Kris