Another extension is calculating tax

Magento lets only one extension calculate sales tax. There is no priority setting and no way to rank providers: whichever extension claims tax calculation wins outright, and every other one goes quiet.

If a second tax extension is installed alongside TaxCloud — Avalara, Vertex, TaxJar, Sovos, or a tax customisation your agency wrote — it may be the one calculating. TaxCloud then still shows as installed, still shows as Enabled, and Verify Credentials still succeeds, because none of those check who is doing the calculating.

This under-collects tax

While another extension is calculating, TaxCloud is not calculating tax and not reporting your sales for filing. Orders keep going through. Nothing on the storefront looks wrong. This is worth checking the moment you suspect it.

How you find out

A banner in the admin. If TaxCloud detects that something else is calculating tax, a red message appears at the top of every admin page naming the extension that has taken over. Follow the link in it back to this page.

You can dismiss that banner once you have read it. It comes back on its own if the situation changes — a different extension takes over, or the same one starts affecting another store view — so dismissing it is safe.

A note in the log. With logging on, an order placed while another extension is calculating writes a line saying TaxCloud is enabled but did not calculate. See Reading the log.

A check you can run. Someone with server access can run:

bin/magento taxcloud:diagnose

It prints, for each store where TaxCloud is enabled, whether TaxCloud is the extension calculating tax and which one is if it is not.

Needs a developer

This is a command line, so hand it to whoever maintains your server or your host. Ask them for the whole output — TaxCloud support can read it directly.

How to fix it

Decide which one you want. Running two tax extensions is not supported by Magento and one of them will always lose. Pick one.

If you want TaxCloud: remove or disable the other extension. Your developer or host does this — disabling it in the admin is usually not enough, because the conflict is in how the extension is installed, not in its settings.

If you want the other one on some stores only: turn TaxCloud off for those store views instead of leaving it on and losing. Stores → Configuration → Sales → Tax → TaxCloud Settings → Enabled, with the store view picked at the top left. TaxCloud stops warning about a store where it is switched off. See Multi-store setups.

If both must stay installed: a developer can make Magento load TaxCloud after the other extension so TaxCloud wins. This is a code change to the extension, not a setting, and it has to name the specific extension you are conflicting with. Give them this, replacing the module name with the one the banner or taxcloud:diagnose reported:

<!-- app/code/Taxcloud/Magento2/etc/module.xml -->
<sequence>
  <module name="Magento_Sales"/>
  <module name="TheOther_TaxModule"/>
</sequence>

Needs a developer

Adding an extension there that is not installed does nothing, so this is safe — but it only helps against the extension actually named, and it has to be re-applied when TaxCloud is upgraded. Removing the conflicting extension is the durable fix.

What the check does not tell you

A clean result means TaxCloud is the extension calculating your tax. It does not mean your tax is right. Credentials, addresses, TICs and fallback all still matter — see Common problems if tax is wrong rather than missing.