I'm here to help fix the issue you encounter with the invoice format.
I want to make sure that the steps I'll be providing fits with what you encounter. Thus, I need more details about your concern. Are you trying to print the invoice? Or are you trying to email it to your customer? Else, are you trying to review the invoice transaction? I'll also appreciate it if you can share a screenshot.
In the meantime, let's open the invoice on an incognito window to isolate any browser-related issues. You can use these keyboard shortcuts to open one:
Google Chrome: Ctrl + Shift + N
Microsoft Edge & Mozilla Firefox: Ctrl + Shift + P
Safari: Control + Option + P
If the text are now readable, you can go back to a regular browser and clear its cache. Piled internet browsing history can also be the reason for some unexpected issues on the opened pages. You can also use a different browser like Microsoft Edge, Mozilla Firefox, Safari, or Google Chrome.