Connecting DATEV

Prerequisites

• A DATEV Unternehmen Online (DUO) account
• Access granted by your tax advisor (Steuerberater)
• Confirmation from your tax advisor of which Mandant (client) you should connect — your consultant number (Beraternummer) and client number (Mandantennummer)

Steps

1. Check with your tax advisor which Mandant you should connect

   • Your tax advisor can confirm your consultant number (Beraternummer) and your client number (Mandantennummer)
   • Together they identify the Mandant as {consultant_number}-{client_number} — for example 455148-2
   • You do not type this value in by hand: DATEV returns the Mandanten you have access to and you pick one from a list (step 4). Knowing the numbers up front just tells you which entry to pick.

2. Select your environment

   • This connector currently only functions against DATEV's Sandbox — select that option before you authorize. Production is offered in the setting but is not yet supported: authorizing and connecting still reach DATEV's sandbox regardless of which value you pick.

3. Authorize the connection

   • Click "Connect" in Apideck Vault
   • You will be redirected to DATEV's login page
   • Log in with your DATEV credentials (Benutzerkonto)
   • Grant access to the requested scopes

4. Select your DATEV Client (Mandant)

   • After authorizing, open the connection settings and use the DATEV Client (Mandant) dropdown
   • The list is fetched live from DATEV and shows the Mandanten your DATEV user has access to, in the plain 455148-2 form
   • Optionally set Fiscal Year Start if your fiscal year does not begin on January 1 — it is used to work out the fiscal year for reads such as the balance sheet

Settings

Setting	Required	Description
Environment	Yes	Sandbox or Production. Must be set before you authorize. Only Sandbox is currently functional (see Steps above).
DATEV Client (Mandant)	No	The Mandant to connect to, picked from a dropdown that DATEV populates after you authorize (for example 455148-2)
Fiscal Year Start	No	Start date of your fiscal year (YYYY-MM-DD). Defaults to January 1 of the current year.

Important notes

• Bidirectional: This connector reads accounting data FROM DATEV and writes data TO DATEV.
• Async processing: Journal entries and master data uploads are processed asynchronously by DATEV. There may be a delay before they appear in your tax advisor's system.
• EXTF format: Journal entries are automatically converted to DATEV's EXTF CSV format.
• Write support is still being hardened: Reading accounting data works as described above. Creating journal entries, customers and suppliers is a supported capability that is not yet verified working end-to-end — see Troubleshooting below if a write is rejected.

Troubleshooting

Issue	Solution
"Unauthorized" after connecting	Apideck refreshes DATEV access tokens automatically (they are valid for 15 minutes). If the error persists, the underlying DATEV authorization has ended or been revoked — reconnect.
The DATEV Client (Mandant) dropdown is empty	The list comes from a live call to DATEV, so it only fills in after you have authorized successfully. Ask your tax advisor to confirm your DATEV user has access to the Mandant.
"Client not found"	Re-open the DATEV Client (Mandant) dropdown and select the Mandant from the list rather than supplying a value yourself. The values DATEV returns are the plain consultant-client form, for example 455148-2.
Journal entries not appearing	DATEV processes uploads asynchronously. Wait a few minutes and check with your tax advisor.
A create is rejected by DATEV	Write operations (journal entries, customer and supplier master data) are still being hardened and are not yet verified working end-to-end. Reads are unaffected. Report the failing operation to Apideck Support so it can be tracked against the open work.

Still stuck? Contact Apideck Support.