There are also enterprise offerings with recurring payments: https://work.threema.ch/ https://work.threema.ch/ If you take a look at the customer list (Daimler

There are also enterprise offerings with recurring payments: https://work.threema.ch/ https://work.threema.ch/ If you take a look at the customer list (Daimler with 300k employees, Bosch with 400k employees, the federal administration of Switzerland, and others) it does seem to be quite a sustainable business model. (Edit: Added note about customer list)