Error message: 553 Relaying disallowed

Error message: 553 Relaying disallowed

I'm facing a problem with Zoho.

I can send emails via Zoho mail but I don't receive incoming emails from Squarespace - my domain is themuseumcreative.com.

I tried to send a test email from my Gmail account to my Zoho email, and I got this message:
The remote server is misconfigured.
553 Relaying disallowed.

Can you please check and let me know what to do to get this problem solved?

Thanks