Illegal characters in POST. Possible email injection attempt

i have a form on my website,
and for some reason when a user submit URL i see “Illegal characters in POST. Possible email injection attempt”.
can you investigate ?

https://monkeewonkey.bandcamp.com/album/west-of-kalahari-going-south-part-ll-into-the-valley

the site URL to test is here https://pastebin.com/n3tvQJ1p
i don’t want to save my site URL visible here.

The page I need help with: [log in to see the link]