Get your Colorado Revenue Online accounts through an API

What you can build on Revenue Online

• Get account balances

  Build this

  Reads the balance on each tax account you can see after logging in to Revenue Online, such as sales tax and withholding, with the period it belongs to.

  Takes

  Account type (optional)

  Returns

  Account type, account number, filing period, balance due

• Get letters from the Department

  Build this

  Reads the list of letters the Department has sent for your tax accounts in Revenue Online, with each letter's date, title and account.

  Takes

  Sent since (optional)

  Returns

  Letter date, letter ID, title, account type, account number

• Get payment history

  Build this

  Reads the payments recorded on one tax account in Revenue Online: when each was received and which period it was applied to.

  Takes

  Account number, received since (optional)

  Returns

  Payment date, filing period, amount, payment type

• File a zero sales tax return for a location

  Build this

  Clicks File Return on a sales tax account, opens the Retail Sales Return, ticks $0.00 gross sales for one Location ID and submits on Confirm Return.

  Takes

  Account number, Location ID, filing period

  Returns

  Confirmation, Location ID, filing period, filed date

Automate Revenue Online with a workflow

A workflow runs your methods as one process, with nobody at the screen. A schedule or a call from your own system starts it, the steps run in order, and the result arrives in your inbox or in the systems you already use.

• New letters from the Department, every morning

  Build this

  Starts

  Every weekday at 7:00 Mountain Time

  Step 1

  Get the letters from the Department for all your tax accounts.

  Step 2

  Keep the letters that were not there on the last run.

  Step 3

  Email you each new letter's date, title and account.

• Balances due on your tax accounts, weekly

  Build this

  Starts

  Every Monday at 8:00 Mountain Time

  Step 1

  Get the account balances for every tax account.

  Step 2

  Keep the accounts with a balance due above zero.

  Step 3

  Email you the list, or stop the run when nothing is owed.

• Payments applied, posted to your accounting system

  Build this

  Starts

  On the 25th of every month at 9:00 Mountain Time

  Step 1

  For each sales tax and withholding account, get the payment history since last month.

  Step 2

  Keep the payments that were not there on the last run.

  Step 3

  Post account number, payment date, filing period and amount to your accounting webhook.

You can run a workflow by hand on every plan, Free included. Schedules and webhook triggers come with the paid plans, from $29 a month.

Once built, one call from your code

Once you have built a method, it is one POST to /v1/runs from your backend, or a tool an AI agent calls over MCP. This is what “Get account balances” would look like.

curl https://api.fous.com/v1/runs \
  -H "Authorization: Bearer $FOUS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "method": "colorado.gov/get_account_balances",
    "input": {
      "account_type": "Sales Tax"
    }
  }'

{
  "status": "completed",
  "data": {
    "accounts": [
      {
        "account_type": "Sales Tax",
        "account_number": "00000000-0001",
        "periods_with_balance": [
          {
            "filing_period": "2026-09",
            "balance_due": 412.37,
            "currency": "USD"
          }
        ]
      }
    ],
    "count": 1
  }
}

An example with invented data, not a ready-made endpoint. The method exists in your organization once you build it, and its name, inputs and fields follow your request.

Revenue Online’s own options

The Department offers no API for Revenue Online accounts. Retailers with several locations can e-file sales tax returns as XML through software the Department has tested and approved, or upload an Excel spreadsheet after the Department approves a sample. Balances, payment history and letters are read in Revenue Online after logging in.

Read on November 12, 2026: Software Developers: Sales Tax XML, Sales Tax Spreadsheet E-Filing, File Sales Tax on Revenue Online.

Signing in to Revenue Online

Revenue Online signs you in with a username and password, asks for a one-time security code the first time and, with two-step verification on, at each login. Each tax account is added with the Letter ID that comes with its license. With Fous you sign in once through Revenue Online's own sign-in with your own login: it is sealed with AES-256, never returned by the API, and an expired session is signed back in.

Worth knowing

One return per location

A retailer with more than one business location files a separate sales tax return for each location in Revenue Online. A method that files takes the location as an input.

Self-collected cities are filed elsewhere

Sales and use tax owed to self-collected home-rule cities cannot be filed in Revenue Online. It goes through the Sales & Use Tax System (SUTS) or straight to the city.

File even when nothing was sold

A sales tax return is due every filing period, even with no sales and no tax collected. Each physical Location ID is opened and confirmed, and the remaining non-physical sites can be filed as $0 returns in one step.

A missed period gets an estimated return

If a return is not filed, the Department files one for you with an estimated amount. It stays due and payable until you file the actual return.

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