client's icloud.com email is "invalid"

I can't input my client into the software because his email

galvezronald21@icloud.com  comes up as "invlaid" even though

i have been communicating with him for some time on my work

email account and I know he receives my emails.

I am supposed to see him tomorrow (Sunday) virtually.

Please help me with this issue as soon as possible.  

Thanks, Margaret