Zoho writer mail merge one of two recipients not reached

Zoho writer mail merge one of two recipients not reached

I have a spreadsheet with two rows of addresses which I import as data in a mail merge in a Zoho Writer document. The preview is fine, but when I send it, one of the two recipients is never reached. The address is fine, and I can reach that person by Zoho mail without fail. The order of the rows in the sheet is irrelevant. I haven't tried with more addresses yet.
I'm at my wits end