Subject: {{first_name}}, trying to connect with you

Hello {{first_name}},
Unfortunately, I couldn’t get in touch with you on the phone earlier today. I was calling to discuss [[insert the brief description of the offer]].
However, the voicemail told me to try reaching you again [[enter the date and the time]]. Till I do, you can contact me here or at [[insert a cell number]].

[[your signature]]