You've understood it right: it's mandatory to configure DATEV UO correctly before using Spendesk's native integration with DATEV. Here is a recap of the steps to be followed:
To subscribe to Rechnungsdatenservice 1.0, you should proceed with the processing form set up as "Erweitert" in DATEV UO.
👉 In DATEV UO, clients can be created with two different processing forms: "Standard" or "Erweitert". This provides different levels of permissions. If you want to learn more about "Rechnungsdatenservice 1.0" check out this link.
As Spendesk uses Rechnungsdatenservice 1.0 to export data to DATEV, you will need to subscribe to Rechnungsdatenservice 1.0 prior to synchronizing Spendesk with DATEV.
🚨If you don't do the above, then you will experience connection issues when trying to synchronize Spendesk with DATEV. 🚨
DATEV has a dedicated support for your company's tax consultants which is free of charge to help them set up DATEV UO for Spendesk integration. They can book a time slot here: https://www.terminland.de/datev-partner-onboarding/