Problem with Brute-force

Hello all,
I am in despair…
I have been trying to solve the problem for HOURS:

I changed my password and my apps like DavX tried to access with the old password. Now the error message: “We have detected multiple invalid login” appeared in the login screen.

Despite repeated logins of all users, the message did not go away.
I found out that the program Bruteforce is responsible for this. But no matter which direction I tried… nowhere was there a simple solution!

I often read about MySQL but I have no idea about MySQL at all.

I finally installed the app “Brute-Force IP-Whitelist” and was already happy that there must be a simple solution.
But no, I don’t understand the IP address! I don’t know what this slash “/” is all about, I did try to find out on the internet what kind of IP address this is, but I just didn’t really figure it out.

Please help me, how do I find out my IP address with this “/”? Or is there any other solution to reset the IP lists in Bruteforce?

I have Nextcloud installed on my Rapsberry PI 4 with Nextcloud Pi.