If you have a discounted freight rule, via the Free/Discounted if order total over: option in the settings you can reword the default prompt.
By default the prompt will say for an example 'Spend $35 more to get FREE SHIPPING' which is incorrect if only discounting.
You can reword this prompt via the DESIGN > REWORD PROMPTS area. As the prompt contains dynamic text e.g. the amount to spend, you need to target with the following rule:
Reword prompt to target with a new phrase: Spend [AMOUNT] more to get FREE SHIPPING