Automate website login where the website only allows manual input of username/PW

Hello,

I'm writing a program where one of the steps is:
Open internet Explorer and navigate to a website > Enter the username and password and press the button "Login".
Now this is working just fine up to the point where the Login button gets pressed.

Even though both the username and password fields are filled properly by my script, the website gives an error message when the Login button is pressed; saying "Username field can't be blank".
If I manually type the username and password at this point it works, which makes me think that this website doesn't allow automated logins somehow?

I wish I could give you the link for this website so you can observe the source code, but that's unfortunately not possible since the site can only be accessed through my workplace's network.

I have played around with different things such as trying to type the username and password using SendKeys without success, all though I would rather avoid using SendKeys.
I also tried letting the script fill the username and password and then use SendKeys to enter 1 letter and then remove it again but I didn't get that to work and it would also feel very unreliable.

Any suggestions are greatly appreciated.


**Edit**
There is one way I have made this work; after the script enter the username it sets focus on the username field and then the same process with the password.
However.. This doesn't work if the script actually clicks the Login button, I have to use SendKeys "{ENTER}" and I want to avoid that.