Sometimes Instagram prevent users from clicking their own link in bio. They do this to prevent users from artificially driving up their stats by clicking on their own links. Instagram may do this to any link in your bio!
The good news is that there's usually nothing wrong with your Milkshake website.
Check if your website is accessible to followers
Use your internet browser to to go your Instagram. Make sure you're logged out so you can see your profile from the point of view of the a follower. When you click on your msha/ke link, your Milkshake website should open without error.
Switch to a different account in the Instagram app (if you have multiple accounts), then view your profile so you can see what everyone else sees. When you click on your msha/ke link your Milkshake website should open without error.
Ask a friend or family member to go to your profile to check your link is working.
Reporting the error to Instagram
If your link is correct but the "Sorry, this page isn't available" message still appears report the issue directly to Instagram.