Suscribe URL Problem

Hello, How are you?

My problem is that I write the link of my subscription page, for example:
https://www.mypage.com/subscription

But when I press the subscribe button it takes me to:
https://www.mypage.com/(page where is the subscription buttom)/www.mypage.com/subscripcion

And this link obviously doesn’t work.

What I can do?

Thanks a lot.

All the best!