Trouble with a custom function in Zoho Flow, API, invokeurl, Gmail, SMTP error

Trouble with a custom function in Zoho Flow, API, invokeurl, Gmail, SMTP error

I am having trouble with a custom function in Zoho Flow, using invokeurl, with send_mail.

Error: "message": "Connectivity issue occurred when sending mail via your SMTP server",

I can get it to send just fine from one email, but not another. In other words. There are only problems with one email "from" address. 

Example code:
sendit = invokeurl
[
type: POST
parameters: param + ""
connection: "zoho_crm_connection"
];

* The connection is good.
* It does not seem to matter who I log in as.
* I created a new connection under the login email that is having trouble. But, that did not fix it. 
* I gave the problem login email admin access to Zoho Flow, Zoho CRM, Zoho Creator.

Also, I can send just fine with the problem email using Notification > Send Mail. But, that method does not link it to the contact. 

We use Gmail, and Zoho Flow is configured under Security > API Controls > Manage Third Party Apps Access. Are there settings in Gmail I can check, for the problem email? 

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