Gradient MSP's Billable has been added as an integration with Mailprotector. The feature provides billing reconciliation to a partner's PSA through the Gradient MSP platform. Gradient MSP works with several more PSA's than Mailprotector does, opening up integration to a wider partner base.
In addition to ConnectWise and Autotask, Gradient MSP supports BMS by Kaseya, Syncro, Pulseway, HaloPSA, Accelo, and Tigerpaw.
The configuration KB article is Integrate with Gradient MSP Billable.