From the issue:

> Supporting Lightning as a payment option is in the backlog for the team managing payment methods. But I can't give any ETA for when that might be available.

They then point out it's the wrong repo to ask this.

> For all non-app related questions and feature requests, please contact support@mullvad.net.

Sounds like cajoling support is the only way :-)

From a privacy point of view, in a world infested with chain anal companies, not supporting lightning is problematic.