Hi there,
I don't see that code listed as an error message on the support site. Are you sending the invites from the Distributions tab or with a Workflow? Could be worth bringing it up to Qualtrics Support.
https://www.qualtrics.com/support/survey-platform/distributions-module/email-distribution/email-distribution-error-messages/

https://community.qualtrics.com/XMcommunity/discussion/comment/44803#Comment_44803Thanks for your reply! The invites are sent from the Distributions tab. I will contact the support team, indeed I have not found this error code anywhere online or in another thread.