If you've built card issuing into your product, what caught you off guard?

If you've integrated card issuing (virtual or physical) into your product, what was the biggest surprise during implementation?

Was it things like:

• Ledger / accounting complexity
• Authorization vs. settlement handling
• Declines and edge cases
• Card lifecycle management (freeze, replace, renew)
• BIN sponsorship/program management
• Compliance requirements
• Customer support volume

What's something you'd plan for much earlier if you were doing it again?