Write a win-back message for a customer who left

A customer stopped buying from me. Write a message to win them back without sounding desperate.

What I know: {{context}}
Why they may have left: {{reason_if_known}}

The message should:
- Be honest and low-pressure.
- Acknowledge it has been a while.
- Give one genuine reason to come back (a change, an improvement, or a fair offer).
- Make it easy to reply or to say no.

Give me two versions: one short and warm, one with a specific offer.