It only occurs when someone has reported your personal message as a spam. Are you advertising via PM or you've been up against someone here in the forum and started to make a war via sending him/her a PM? Someone has probably reported you and it is approved by admin that your PM is a totally spam.
cissrawk is right. It is the only way to unban your account and I'm telling you, there are already some threads/issues about this back in 2017 and having a response to the appeal email really takes some time. And you have a low chance to unban your account unless you have a valid reason.
The thing is that I did not send advertising to the PM and sent no threats. Most likely my messages were regarded as spam. But I did not do anything unusual. Everything is as usual. And in general, I rarely write messages.