Authentication problem

[Shelly]

For the last 2 days my wifi wont connect, its saying authentication problem. I've gone through several things with my wifi box and my S9 but I'm getting very frustrated now. The only thing I haven't done is a factory reset and I would love to avoid this. Any suggestions or anyone had this happen or is this am issue with the Samsung S9?

[Bambino]

@Shelly If you list the things you've done with your WiFi and phone, someone may be able to help without offering what you've already done.

Edit: Have you spoken to Samsung support? https://www.samsung.com/uk/support/

[Shelly]

Thanks Bambino.
I've turned my wifi off and on.
Tried to reconnect wifi.
Forgot wifi and then connected again with password.
Done a reset by pressing the power button and volume button.
Then power button and Bixby.
Checked for updates.
I've checked my other devices and they all connect with my wifi.
I've not spoken to Samsung yet, I was going to give them a call tomorrow and possibly go down to the shop but they won't be able to see the problem.

[liggerz87]

Have a look for the app called Samsung member that has diagnostic tools and also a way to speak to samsung

[MI5]

In all honesty, this is usually the wrong password. Are you 100% sure you're trying the correct one?

[Shelly]

I have it written down everywhere and then even checked the back of my box to make sure and its correct.

[Bambino]

@Shelly Samsung support is still your best bet. Have you contacted them yet?

[anticpated]

There is a couple of things it can be.  The chosen authentication doesn't match the routers setting or the password is incorrect with an incorrect lower or higher case character or digit (also be aware whitespace is considered as a valid character). Sometimes the Wi-Fi cache works better if you 'forget' the previous setting completely on the receiving device (the Samsung) and try to create a new connection it sometimes works.

Essentially you want to choose WPA2 mode (auto) and avoid using WPS as it allows you connect wirelessly on the fly, so not the best for security. 

https://www.netspotapp.com/wifi-encryption-and-security.html

It's a complicated subject but in principal it's all about radio channels, encryption and broadcast frequencies (2.4Ghz or 5Ghz).

My answer might seem over the top but I think understanding to some degree how something is meant to work solves at least 50% of the problem.