Do I need to raise my Shopify spending limit for additional usage?

If your workspace is billed through Shopify, yes. Shopify only charges up to the monthly spending limit you approved, so the limit has to cover your users plus any additional tickets, chatbot sessions and extended retention you approve. When the limit is too low, the Plans page shows your current Shopify limit and the limit you need, with a button that takes you to Shopify to approve the new amount. Approving additional usage in Deskhero does not by itself raise the Shopify limit.