Using parameters to get data from dynamic url

Hello,

I have not been able to find a solution to my problem even tho there are similar solved problems in this forum.

What I am trying to do is use parameters (from cell*s or table*s) in an url.

To define the parameters I tried two different solutions.

The first one was to write the value in a table and get the value via a Query.

It looks like this:

let
    Source = Excel.CurrentWorkbook(){[Name="TestenParams"]}[Content],
    TestParam1 = Record.Field(Source{0},"Start")
in
    TestParam1

The other one was defined by using the built-in option of the Power Query Editor.

I would prefer to use the first variant but for testing purposes I tried both.

The next step was trying to replace a part of the url with the parameter.

A simplified example of the important part of the Query would look like this:

let
    TestParam1 = Start,
    Source = Json.Document(Web.Contents("https://someurl.com/somecategory/64dfg8d484-4fsd4-fwewtg1w8/records?fromHere="&TestParam1&"&toHere=1525426100", [Headers=[Accept="*/*", #"Content-Type"="application/json"]])),
    #"Converted to Table" = Record.ToTable(Source),

For some reason I have not been able to create a working url using parameters.

Most of the time I get the "Expression.Error: We cannot apply operator & to types Text and Number" error.

Why am I not able to use parameters this way?

Thank you.

LPLA