Plugin hangs on login

I had the Sendinblue plugin installed and activated on my WP site. I noticed it wasn’t syncing senders I’d added to my Sendinblue account, so I tried refreshing and logging in and out of WP admin. None of that worked, so I tried logging out from the Sendinblue plugin. Then, I couldn’t log back in because after entering the API Key, it said the plugin was activated and then just stayed on the API Key intro/login page. Finally, I deleted and reinstalled the plugin. Now, when I enter the full API key, I click “Login” and it just hangs forever. Please help!