I am using the Mailpoet as my sending service. Maybe this can help.
I paused sending newsletters for a while back. Within the time, I made an update to my server’s php version. WordPress got affected, but I later resolved it. That was in 2023.
At the beginning of this year, I resumed sending newsletters and, on my first attempt, this is the issue I’m facing.
I hope you understand my issue clearly now. Any help?