Created attachment 37720 [details]
Simple example for testing

Using the GraphQL HTTP Request sampler with Variables set like this:

{
	"number": ${number}
}

(Note no " around the value)

Results in the following error:

2021-01-26 17:07:23,695 ERROR o.a.j.p.h.u.GraphQLRequestParamUtils: Ignoring the GraphQL query variables content due to the syntax error: Unrecognized token '$': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
 at [Source: (String)"{
	"number": ${number}
}
"; line: 2, column: 13]

And the POST Data is missing the variables:

POST data:
{"operationName":"Test","query":"query Test() {\n\t\n}"}

Adding quotes gives the expected behaviour:

POST data:
{"operationName":"Test","variables":{"number":"0"},"query":"query Test() {\n\t\n}"}

But the value is now passed as a string instead of a number, so is not the correct request.