JWT assertion Error

Dear Anyone,

I am currently trying to execute Box API that uses JWT,

But the following issue occurred when executing the Box API to obtain an access token.

I get an error stating that the JWT is an invalid value, but when I check with jwt.io I can see that it is a valid value.

If someone else has sent a support request asking about the same issue and it has been resolved,

or alternative solutions you may suggest would be highly appreciated.

[Error details]　*This is written in the body of the HTTP response.

body: "{"error":"invalid_grant","error_description":"Signature verification failed"}"

・Confirmed JWT in jwt.io

Thank you very much in advance for your assistance.