Files saved on Zoho Invoice as XLSX (good) but when accessed/downloaded they are converted to .txt--HELP

Files saved on Zoho Invoice as XLSX (good) but when accessed/downloaded they are converted to .txt--HELP

Love Zoho Invoice. But here's a question: when I invoice clients monthly, I push an invoice with invoice detail from excel. The excel is saved to Zoho Invoice as an .xlsx file and it sends to the client correctly. The issue is that later, when I go to access to attachment easily, the attachment saved WITH the invoice has been converted to a .txt file. Is there a Zoho Invoice developer that can look into this and correct it? Otherwise I have to dig through emails to find the invoice and its attachment...and that isn't the point of having it all in once location. Thanks!