Redirecting with clicked link, React, RRD6 - reactjs

Question

sorry about title name, i cant name my problem, but basically: My navbar dropdown menu looks like this:
Home Dropdown 🠗 Contact
Sign In
Register
Problem is, when somebody clicks on SignIn and then clicks on Register (and conversely), the url will look like this: http://localhost:3000/signupform/signin so browser will tell that this page does not exist.
But it should look like that: http://localhost:3000/signupform
Thanks everybody so much.
Navbar code (without imports):
const Navbar = () => {
const [isMenu, setisMenu] = useState(false);
const [isResponsiveclose, setResponsiveclose] = useState(false);
const toggleClass = () => {
setisMenu(isMenu === false ? true : false);
setResponsiveclose(isResponsiveclose === false ? true : false);
};
let boxClass = ["main-menu menu-right menuq1"];
if(isMenu) {
boxClass.push('menuq2');
}else{
boxClass.push('');
}
const [isMenuSubMenu, setMenuSubMenu] = useState(false);
const toggleSubmenu = () => {
setMenuSubMenu(isMenuSubMenu === false ? true : false);
};
let boxClassSubMenu = ["sub__menus"];
if(isMenuSubMenu) {
boxClassSubMenu.push('sub__menus__Active');
}else {
boxClassSubMenu.push('');
}
return (
<header>
<nav>
<div className="container">
<div className="row">
<div className="header__middle__logo">
<Link to exact activeClassName='is-active' to="/">
<FontAwesomeIcon icon={faMagnifyingGlass} size="4x" color="white" alt="logo" />
</Link>
</div>
<div className="header__middle__menus">
<nav className="main-nav " >
{/* Responsive Menu Button */}
{isResponsiveclose === true ? <>
<span className="menubar__button" style={{ display: 'none' }} onClick={toggleClass} > <FiXCircle /> </span>
</> : <>
<span className="menubar__button" style={{ display: 'none' }} onClick={toggleClass} > <FiAlignRight /> </span>
</>}
<ul className={boxClass.join(' ')}>
<li className="menu-item" >
<Link to exact activeClassName='is-active' onClick={toggleClass} to={`/`}> Home </Link>
</li>
<li className="menu-item " ><Link onClick={toggleClass} activeClassName='is-active' to={`/contact`}> </Link> </li>
<li onClick={toggleSubmenu} className="menu-item sub__menus__arrows" > <Link to="#"> Sign <FiChevronDown /> </Link>
<ul className={boxClassSubMenu.join(' ')} >
<li> <Link onClick={toggleClass} activeClassName='is-active' to={`signin`}> Přihlásit se </Link> </li>
<li><Link onClick={toggleClass} activeClassName='is-active' to={`signupform`}> Registrovat se </Link> </li>
</ul>
</li>
<li className="menu-item " ><Link onClick={toggleClass} activeClassName='is-active' to={`/Contact`}> Contact </Link> </li>
</ul>
</nav>
</div>
</div>
</div>
</nav>
</header>