I have looked carefully at all the URLs and can't figure out which one might be invalid.
Any suggestions about how to resolve this issue??
I can't save my work because of this issue.
Hello @WPLCA1. I'm sorry that you are seeing this error when trying to save your block. Usually we see this message appear when text is pasted into a block and some problematic formatting is carried over into the HTML. Did you happen to paste text into this block? If you were pasting text into your email, we recommend first copying and pasting this text first into a text editor to remove the problematic formatting. You can then bring this stripped text into your block and save it.