Why can't I email this notice through Kera?

Read the line under the serve choices; it names the cause:

1. "Kera can't email it: <Name> doesn't accept online notices. Serve it another way.": a tenant without a Kera account and no lease-level consent. Use Open the lease to turn on the lease's setting (if their lease or a written agreement allows it), or confirm it from the Serve step.
2. "<Name> turned off email notices in Kera. Serve <first name> another way.": the tenant switched it off in their portal. Only they can turn it back on.
3. A tenant with no email address: add one on the tenant record.
4. The province doesn't allow it, or Kera can't be the sender (Nova Scotia).