I found the issue. If you have auto-fill, your browser sees the API box as a field it wants to auto-fill.
Sendgrid’s plugin automatically updates when there’s content in there.
Result – your browser keeps putting info in there, Sendgrid’s plugin keeps refreshing… it keeps looping and breaking.
HOW TO FIX:
I opened it in incognitomode (where there was no auto-fill) and put everything. Works now. And I’m aware you might have moved on already, but this is for anyone who needs help.
Today I have the same problem.
I disabled the password save in my site, and then I can config it.
Is a great plugin, but nobody knows if they cannot use it!
