You are managing an email in Sphere. It may be a confirmation email, eNewsletter, or Communcations>Email. After clicking Save, the following message is displayed:
One or more of the merge field names you entered is not valid. To save the content, update the fields or remove them from the message.
First, ensure only merge fields which are specific to that mailing are included in the content. For example, you are editing a donation confirmation, but copied and pasted a merge field from a registration confirmation email.
Next, convert the HTML to Text via:
From the content of your mailing, click the Text Button
Click the Convert HTML to text Hyperlink
Click Submit in the popup window
If the error message persists, remove all the fields and re-add them, then convert HTML to Text. You may also attempt removing/adding one field at a time, though ensure HTML to Text conversion takes place after each edit.