Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I understand that you are facing issues with a website.
I take it that https://tax.delaware.gov/ is a third-party site and you do not have access to it.
It appears that the third-party site is behind an Azure Application gateway.
And the third-party site has Forbidden your request.
Note that Azure App Gateway is only acting as a web traffic load balancer here and the requests are still coming from the third-party site.
You should raise this issue with the third-party site to get this resolved.
Thanks,
Kapil