After upgrading spark, did you update the package.json file with what they said here: https://spark.laravel.com/releases and also rerun npm install and npm run dev?
Spark v4: Error sending team invitations
Just upgraded to version 4.0.7 and I'm getting an 500 server error at the moment of send an invitation to a new member team.
I previously setup my mail driver to mailgun but appears to be a problem with ajax post on this route: https://{domain}.dev/settings/teams/1/invitations
This error appears on javascript console:

UPDATE: Invitation records on database are created successfully, email not sent.
It was a missconfiguration with mailgun's secret key, my fault!
Laravel or Spark must handle ClientException in RequestException and display a flash message?
Because invitation it was created, but incomplete due a missing email.
@briang sorry for a late response, your comment helped me to remember uncheck my filters in debug tool
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