How do i create a dynamic URL in Powerbi source query

I am trying to load data from Log analytics and i am i want to create dynamic URLS for each customer when i open PBIT template file.

eg --> let Source = Json.Document(Web.Contents("https://api.loganalytics.io/v1/workspaces/WORKSPACEID/query", 

I want WORKSPACEID to be dynamic. I tried two methods

1. Reading the WORKSPACEID from text file and ( i have a per customer folder so, chosing right file is taken cared of using the parameterised path to file)

2. Using this, i created an additional query to extract only WORKSPACEID.

= let Source = Json.Document(Web.Contents( "https://api.loganalytics.io/v1/workspaces/"& "#LAWorkspace" &"/query",

When i use this query name in the Main query to log analytics, it throws error.

Expression.Error: We cannot apply operator & to types Text and List.

I also tried creating a new table with all WORKSPACE ID's and customer name mapping and tried to using ID from this table , even this fails.

"Expression.Error: We cannot apply operator & to types Text and List."

let Source = Json.Document(Web.Contents("https://api.loganalytics.io/v1/workspaces/" & WorkspaceID & "/query",

Any help would be appreciated, already spent a day , going crazy 😞