I'm trying to create a Jira Issue in testlink. All configs have been set, however I did not add version to the configuration in testlink itself, it didn't seem necessary.
I've set fix versions in Jira.
What other configurations might be the issue when receiving this error?
You need to make sure that this field appears on the issue screen (when you edit and create an issue from Jira, you can see this field).
If this is the case, go to Settings (gear icon in the top right corner) -> issues -> screens -> find your appropriate screen and add the field.