When I send an email from my Zoho account ( sam@sam-xcx.com) to my gmail, it goes through. When I send an email from gmail to Zoho, it says that the address was not found and my message was unable to be delivered.

I've checked through third party sites and it says that my MX is linked to Zoho. I also have used the same process and domain hosting company for another Zoho email account and it has went through before. How do I fix this?