Axios accepts only static url - node.js

Question

I'm writing a NodeJS Backend with express and axios where I fetch data from Strapi CMS and send a server-side-rendered HTML-document to the client.
There I encountered the strange behaviour that the first piece of code gets a response from strapi with data.data.length = 0, which isn't expected. The second piece of code returns data.data.length = 1, which is the same as I retrieve with Postman. I can't find the difference since both url's compile to the same string. My expectation is that both requests should be returning the same response.
app.get(`/blog/:URL_Identifier`, async (req, res) => {
let data;
let params = req.params;
console.log(params.URL_Identifier);
let string = hostname + ":" + strapiport + `/api/blogposts?filters[URL_Identifier][$in][0]=${params.URL_Identifier}&populate=*`;
//string prints to https://127.0.0.1:1337/api/blogposts?filters[URL_Identifier][$in][0]=Blogpost1&populate=*
data = await axios.get(string, {
headers: {
'Authorization': 'Bearer ' + token
}
});
//data = JSON.parse(data.data);
console.log(data);
res.render('pages/post', {
data: data
})
})
Whereas the following code returns a data.data.length = 1 with the expected data inside.
data = await axios.get("https://127.0.0.1:1337/api/blogposts?filters[URL_Identifier][$in][0]=Blogpost1&populate=*", {
headers: {
'Authorization': 'Bearer ' + token
}
});
Is this a bug in Axios? I can't see the difference...
EDIT:
I tried the same with the http module from node and found out, thatthe request object from express might be the issue.
app.get(`/blog/:URL_Identifier`, async (req, res) => {
let data;
let doesWork = "http://127.0.0.1:1337/api/blogposts?filters[URL_Identifier][$in][0]=Blogpost1&populate=*";
let doesNotWork = `http://127.0.0.1:1337/api/blogposts?filters[URL_Identifier][$in][0]=${req.params}&populate=*`;
var options = {
headers: {
'Authorization': 'Bearer ' + token
}
};
callback = function(response) {
var str = ''
response.on('data', function (chunk) {
str += chunk;
});
response.on('end', function () {
console.log(str);
data = JSON.parse(str);
console.log(data);
});
}
var req1 = await http.request(doesNotWork, options, callback);
req1.end();
This still gets me this as response
{
data: [],
meta: { pagination: { page: 1, pageSize: 25, pageCount: 0, total: 0 } }
}
Whereas var req1 = await http.request(doesWork, options, callback);
gets me
{
data: [ { id: 1, attributes: [Object] } ],
meta: { pagination: { page: 1, pageSize: 25, pageCount: 1, total: 1 } }
}