You still have the option to change the text but whatever you write will not show.
Hi there! That definitely shouldn’t be the case. I recommend that you get in touch with our customer care team so they can get you sorted 
Hi,
1- Save first,
2- then turn off and on
3- If not, turn your computer off and on.
4- It may be caused by the browser.
Thank you for your answers!
I have contacted the support. The Button text is not modifiable for the checkout button.
The text in the photo is for an another button.
Thanks for updating us on the solution