I’m trying to add Greeny Host’s nameservers to my domain registrar but it’s refusing, how can I resolve this? There’s no spaces between….

Thanks for getting in touch, Are you sure there isn’t a space between [ns1] and [.] like this: ns1 .greenyhost.com ?
Can you please try to add only first and second nameservers? ns1.stackdns.com ns2.stackdns.com Kindly try this:
ns1.stackdns.com
ns2.stackdns.com
ns3.stackdns.com
ns4.stackdns.com

If it doesn’t work, then you need to contact the domain registrar’s support. I see that this domain assisjuniowm.com.br is not purchased yet so how do you want to point it to our servers !!?