GET request not working with variables

So I am making a post request where I provide an endpoint and a body where I have a username and a password. From that post activity I get as an output a header from where I extract a key and a value witch I have to use later for the get method. My key is static but my value is changing every 12 hours. In the previous picture you can see I tried to put the key and the value in two variables so they can change when needed. When i try to do the get request and put my variables in the hearted section is not working and I don’t understand why it won’t accept a variable. Everything is working as it should except the get request.

You are trying to pass a 2-d array to string parameter Just pass a string type data