OSS return filed by your tax adviser: what to agree first

Yes, your tax adviser (Steuerberater) may file the OSS return for you. German law refers the OSS scheme to the general rules on authorised representatives (section 18j(7) UStG, section 80 AO). The return stays yours all the same: you are the business that owes it. So agree four things first: the power of attorney, the portal access, who receives the post and who pays.

Last updated: October 27, 2026

In brief

Allowed: You may be represented by an authorised agent in the tax procedure (section 80(1) AO). For tax advisers, proper authorisation is presumed (section 80(2) AO).
You remain the obliged party: The law puts the duty to send the return and pay the tax on the business (section 18j(4) UStG). A business that repeatedly fails to meet these duties on time is excluded from the scheme (section 18j(6) UStG), and that affects you.
Access: Logging in to the BZStOnline portal needs a certificate. The BZSt pages on the OSS describe no separate route for advisers. Ask your adviser how they log in.
Cost: How an adviser bills is covered in What does a tax adviser charge for an OSS return?.

May the tax adviser file the OSS return?

Yes. Two sources show it:

The law applies the rules on authorised representatives to the scheme: where the notification goes to the BZSt and the BZSt passes the returns on to the other member state, section 80 AO applies, among other provisions (section 18j(7) UStG). For businesses established in Germany this is the usual route, as they can only notify participation in Germany (section 18j(2) UStG).
The Munich tax adviser chamber writes that the scheme lets taxpayers and their tax advisers meet all their cross-border VAT duties at one central point.

Under section 80(1) AO the power of attorney covers "all procedural acts in the administrative procedure" unless its content says otherwise. As a rule that includes the notification of participation and the quarterly return. It does not cover receiving tax refunds.

What does the power of attorney settle?

When your adviser acts for you, these rules of section 80 AO apply:

Presumption: For tax advisers, lawyers and the other persons and bodies named in sections 3, 4 and 4c(2) of the Tax Advisers Act, proper authorisation is presumed (subsection 2). The BZSt may still ask for proof of the power of attorney even without a particular reason (subsection 3). Keep it ready in writing.
Scope: It covers all procedural acts unless its content says otherwise. If you want to limit it, for example to the return and not the registration, write that in.
Revocation: Towards the tax authority a revocation takes effect only when it reaches the authority (subsection 1). If you change adviser, tell the BZSt yourself.
Post: If an authorised agent is appointed, the authority should contact the agent. If it contacts you, the agent should be informed (subsection 5). Agree that you get copies of everything.
Who may help: Someone who gives tax help on a commercial basis without being authorised to do so is rejected (subsection 7). This is no issue with tax advisers. With other providers, ask whether they are authorised (sections 2 and 3 of the Tax Advisers Act).

What access does the adviser need in the BZSt portal?

The BZSt describes the scheme from the business's point of view: participation is applied for electronically in the BZStOnline portal, and the tax returns are sent there too. A certificate is required to log in; an existing ELSTER certificate can be used.

The BZSt pages on the OSS and the portal help that I read on October 27, 2026 name no separate route for advisers, such as a client list or a separate power-of-attorney notification for the OSS. So the honest answer is: settle it with your adviser. They know which access they use in the portal and what the BZSt needs from you for it. If they are unsure, they ask the BZSt.

How the portal and ELSTER relate is explained in OSS return: ELSTER or the BZSt portal?. If you need your own certificate, see Apply for an ELSTER certificate.

What stays with you?

Responsibility for the figures. The details must be given "truthfully to the best of your knowledge and conscience" (section 150(2) AO). You know your transactions best, and the clearer your data arrives, the less your adviser has to ask.
Delivering the data on time. The return is due by the end of the month after the quarter: April 30, July 31, October 31, January 31. A return with no sales still has to be filed, the nil return (BZSt).
The payment. The tax must have reached the Bundeskasse by the end of that month (BZSt). The BZSt gives the payment reference (Kassenzeichen) after the first return, in the BZStOnline portal mailbox, and it goes into the transfer reference together with the quarter. So agree whether you transfer it or your adviser does, and how the payment reference reaches you. More in Paying the OSS return.
The last look before sending. What to look at is in Check your OSS return before filing.

What to hand over for the quarter (reports, credit notes, list of countries) is already in OSS return without a tax adviser, in the section on hiring one.

How to spot an adviser who knows the OSS

A seller writes in the Amazon seller forum: "Beim OSS musste ich meinem Steuerberater quasi sagen was zu tun ist" (with the OSS I more or less had to tell my adviser what to do), for example which accounts to set up to tell domestic supplies and distance sales apart. That is a single voice, not a verdict on a profession. But it shows what you can ask before you start:

Have you filed OSS returns for online sellers before?
How do you separate sales within Germany from distance sales to other EU countries in the books?
What data do you need from me, and by when?
Is your price per quarterly return, and is the registration included?
Who gets the post from the BZSt, and who pays?

How VAT GPT helps

VAT GPT is the tax software for Amazon and eBay sellers in Germany: your OSS return first, then VAT, EÜR, trade tax and income tax, calculated and filed in one place. VAT GPT is not tax advice.

You upload your Amazon and eBay reports as CSV.
VAT GPT breaks the sales down by country and calculates the OSS return for all EU countries.
The overview shows the net amount, VAT rate and VAT amount for each country. With VAT GPT Pro you send the return to the BZSt.

So you have the quarter's figures in order before you hand them to your adviser. There is a Free plan and Go with 30 days free and all Pro features. Try it for free now

Frequently asked questions

Do I have to give my tax adviser a power of attorney? The law provides for representation by an authorised agent (section 80 AO). The BZSt may ask for proof. A written power of attorney protects both of you.

Does the adviser have to sign the return? No. The return is sent electronically in the officially prescribed data format (section 18j(4) UStG). A handwritten signature is needed only where a tax law orders one (section 150(3) AO), and section 18j UStG does not.

Can I take over later? Yes. The duty is yours, and you may revoke the power of attorney. Towards the BZSt the revocation counts only once it reaches it (section 80(1) AO).

Who is liable for a mistake in the return? This page does not answer that; it depends on the engagement and the case. Ask your adviser what the contract says.

What if I am not registered yet? The notification of participation belongs to the same scheme. The steps are in OSS registration in Germany.