I've been trying to install obs-ndi for Linux, and I got to the step of running libndi-get.sh and it generated an error saying access denied.

After a bit of investigating, I found that the download link for the SDK is no longer valid.
NDI now requires a request to be submitted on https://ndi.video/ in order to get access to the SDK download.

The URL that is generated appears to be unique for each user.

Also, the contents of the download is a shell script with an embedded archive.
I'm thinking that the instructions will need to be changed in order to work with the changes NDI has made.

Hope this helps.