No one could help you invite or send request in Bittrex slack. According to their
FAQ :
As of this writing, the Bittrex team is still working on a mechanism for our enhance verified users to be invited to the Bittrex Slack channel. Please check back later for further instructions.
Until now there's no further notice about this, maybe because there have been issues in verification process these past few weeks. Anyway, another option is to contact
chiznitz here in the forum, he seems to be working at Bittrex.