Http post header doesn´t parse the name when it´s a variable

Hi, when I access the http webhook header to put values, I have name/value pair.
The value works well when I choice a variable, but the name doesn´t.
If I put a variable as TokenName with content setted to 'TokenWhats' (for sample) in the http header name, and execute the flow, I get an error:

{
"request": {
"url": "https://sistema......",
"method": "GET",
"headers": {
"{{TokenName}}": "cHxTnsswsZqGvO1U"
},
"timeout": {
"response": 10000
}
},
"response": {
"statusCode": 500,
"data": {
"message": "Error from Typebot server: RequestError: Header name must be a valid HTTP token ["{{tokenname}}"]"
}
}
}