Change Wi-Fi network name

I followed the tutorial to the letter, and it was after clicking on Save Settings that the message

Configuration

An error occurred

Invalid network name (ssid)

In fact, whether it was for the name or the password, I copied the label from the Freebox.

Hello,
I don't know if this is the place:

"It’s here:
http://www.freebox.os.free.fr/"

But so far I haven't found any explanation for my problem. I found the theory that clearly explains how to change the network name and password, but nothing that tells me why when I confirm, a message says that the network name is invalid no matter what the network name is. I need to find a typical FreeBox forum to perhaps get an explanation.

Thank you, I was able to get through the first part without any problem, but I didn't know the technique to change the name and then the password.
I'll try tomorrow morning and I'll keep you informed.

Hello,
Problem:

Configuration

An error has occurred

Invalid network name (ssid)

I tried with a new name, ............... same response
I tried with the old name (the one given by Free when purchasing the box) with the appropriate password ....same response as above

Good evening,
Here are the screenshots.
https://www.zupimages.net/
https://www.zupimages.net/
The name of the network is the new name that appears
I re-entered the name initially given by Free
https://www.zupimages.net/
Then I clicked for a random Wi-Fi key
https://www.zupimages.net/
Then Save and:
https://www.zupimages.net/

Hello,
A long silence following a trip.
I followed Brupala's advice but I'm afraid of making a mistake, as everything is working well and I would like it to remain that way.
When I am on the page: http://mafreebox.freebox.fr/ and I click on Freebox Settings, I'm asked to authorize the application for a password change.
Which password is this about? I want to change the settings (name and password) of the Wi-Fi. Is it referring to those?

Hello,
When I click on Freebox Settings, it asks me if I want to connect.
Answer Yes
Then Guest mode or First connection. Only the second option is accepted.
In this case, I am asked to accept the application for a password change. ?????
Do you want screenshots?

Yes, I have a PC.

Hello;
First photo to talk about the same thing:
https://www.zupimages.net/viewer.php?id=19%2F12%2F3r1b.jpg
Then I choose Freebox Settings:
https://www.zupimages.net/viewer.php?id=19%2F12%2Fkvtz.jpg
I answer YES
https://www.zupimages.net/viewer.php?id=19%2F12%2F0ve3.jpg
I have no choice, only one answer is valid: First connection
https://www.zupimages.net/viewer.php?id=19%2F12%2Fbtb9.jpg

I am certainly not in the right place yet..
Thank you for your patience.

Hello,
As far as possible, I would like to keep the existing passwords.
If the searched name starts with: "fbx.......", I have the corresponding password.
The problem is that Freebox OS opens in guest mode, and I don't have the opportunity to log in.

But I am connected to the PC via the RJ45 Ethernet port.

Hello,
Now that we were starting to go in circles, I decided to call 3244. Fortunately, the number is free from my Freebox because I spent 23 minutes between waiting and the guided manipulations by the technician. Finally, it works.
Here’s the technique: you need to go to the subscriber area, log in with the Free identifier like fbx..... and the corresponding password. Then go to my Freebox, then WiFi settings, I chose the network name, the technician asked me to switch to channel 9 instead of 11, then in security, enter the password, then unplug the box's power supply and restart everything. However, with my smartphone at first it detected my network but had an authentication issue; I just had to remove the name from the list and it automatically reappeared and connected right away.
Thanks again for your help.

I don’t know, the technician told me it wasn't necessary to go through Freebox OS. In the end, it was Malik744's answer that actually applied. What I don't understand is that I didn't succeed when I followed the tutorial which was supposedly the correct one.
There is one strange thing though, after asking me my name and address, the technician announced the name of my network as well as the password which was "clefaleatoire" that I had never chosen. From that point on, everything worked fine. Mystery.