MaxBulk Mailer only accepts secure HTTPS URLs. Tell your webserver to switch from HTTP to HTTPS. Google will no longer index HTTP Sites. Current Safari and Chrome versions are showing security alerts. Right now, using HTTP is not a good idea.
Once your site is secure and using HTTPS, go to the MaxBulk Mailer preferences, second panel and update the MLM URL by replacing 'http://' with 'https://'.
I had already downloaded this version 8.7.2 and even then the problem continued, not to mention that I can only install MLM manually, so I asked for information from where to download the new version of MLM.