Definition
Upselling moves a customer to a bigger version of what they already have: a higher plan, more seats or more usage. Cross-selling offers a different product instead.
When to offer it
At the point of need: when a customer reaches a plan limit, starts using features of a higher plan, or adds more active people. Product events show those moments.
Measuring it
Track upgrade events with the plan they came from and went to, and measure upgrade rate among customers who reached each trigger. Check that upgraded customers keep using what they paid for.