Google token endpoint returning unsupported grant type - node.js

Question

I'm trying to implement Google Oauth to get information on users who sign in with Google such as their name and profile photo.
I found this react library which seems like it can get me a code when using the flow: 'auth_code' param.
Additionally I've found these Google docs which outline how to exchange a code for an ID token which will have user information.
I can successfully retrieve a code using the react component as shown in this slightly redacted log message from my browser:
{
"code": "4/0AWtgzh4VK3QT85egP0m9Rsau_gND-FPDxpM-cPB7ocxTfNkZSCzFSbE86<redacted suffix>",
"scope": "email profile openid https://www.googleapis.com/auth/userinfo.profile https://www.googleapis.com/auth/userinfo.email",
"authuser": "0",
"prompt": "consent"
}
I then send this code to my backend which fires off the following request to the token endpoint as found in the Discovery document, mentioned in the OpenID Google docs:
try {
const resp = await axios.post("https://oauth2.googleapis.com/token", {
code: googleJWT,
client_id: getGoogleClientId(),
client_secret: googleSecret,
redirect_uri: "http://localhost:3000",
grant_type: "authorization_code"
}, {
headers: {
"Content-Type": "application/x-www-form-urlencoded"
}
})
console.log("################## posted", resp)
} catch (e) {
console.log("################## could not post")
console.log(e)
}
However, this results in an error being thrown:
error: 'unsupported_grant_type',
error_description: 'Invalid grant_type: '
even though a grant type of authorization_code is reported as supported by the Discovery document.
For completeness, here's the redacted axios config that gets printed with the above error message:
config: {
transitional: {
silentJSONParsing: true,
forcedJSONParsing: true,
clarifyTimeoutError: false
},
adapter: [Function: httpAdapter],
transformRequest: [ [Function: transformRequest] ],
transformResponse: [ [Function: transformResponse] ],
timeout: 0,
xsrfCookieName: 'XSRF-TOKEN',
xsrfHeaderName: 'X-XSRF-TOKEN',
maxContentLength: -1,
maxBodyLength: -1,
validateStatus: [Function: validateStatus],
headers: {
Accept: 'application/json, text/plain, */*',
'Content-Type': 'application/x-www-form-urlencoded',
'User-Agent': 'axios/0.26.1',
'Content-Length': 298
},
method: 'post',
url: 'https://oauth2.googleapis.com/token',
data: '{"code":"4/0AWtgzh4VK3QT85egP0m9Rsau_gND-FPDxpM-cPB7ocxTfNkZSCzFSbE86<redacted>","client_id":"221274282648-q9nrm8j61s5cba218qot926vnloua2hb.apps.googleusercontent.com","client_secret":"<redacted>","redirect_uri":"http://localhost:3000","grant_type":"authorization_code"}'
},
Why is google complaining that the provided grant type isn't supported and how can I swap this code for an ID token?