You need to pass LinkedIn-Version header as per below example:

# Before
headers: {
  "Content-Type": "application/json",
  Authorization: `Bearer ${req.body.accessToken}`,
},

# Now
headers: {
  "Content-Type": "application/json",
  Authorization: `Bearer ${req.body.accessToken}`,
  "LinkedIn-Version": "202401",
},

How to get LinkedIn-Version from LinkedIn?

Go to https://www.linkedin.com/developers/apps/<appid>/products/share-on-linkedin/endpoints where you need to replace <appid> with you application id provided by linkedin which should look like 224036728.

Then you will get Product version: as per below screenshot which you need to pass while calling api.

source: https://developers.knowivate.com/@kheersagar/a-version-must-be-present-please-specify-a-version-by-adding-the-linkedin-version-header