Sales Tax didnt get calculated

My online store recently went online and everything is going well. Today, as I am reviewing all the Invoices that I have, I noticed that one of the Invoice did not calculated Tax.

The 10th Invoice issued, the SALES TAX did not get calculated. Before and after issuance of 10th Invoice Sales Tax gets calculated just fine. I checked the items to see if the settings are correct and they are.

What is going on? Also, it might be worth mentioning that the items order on this particular 10th Invoice also got ordered and on other invoices, tax is calculated properly. I dont really know what is happening.

I just dont want the same thing to happen again. Any idea why and how?

Look at the address of yor 10th invoice customer. Is that in the Sales-Tax zone?
If not, that is why the tax was excluded.

Hi Louis.

Yes, it is in the sales tax zone.
I have other customers ordering from the same zone and sales tax is calculated.

:dontgetit

I noticed that your "region" field is not a dropdown. Sorry if I ask silly questions but did you check the spelling? Are you sure that all the fields that define your sales-tax zone was correctly spelled when entered by your customer?

Yes, actually if the Zen cart doesnt find any zone that matches what is there on the the database, it will show the dropdown. Then customer can select their region.
I also checked that just in case, the zone is the same.

Ok, lets try something else.

In admin, under "My Store" there are two settings namely "Basis of Product Tax" and "Basis of Shipping Tax". What are your settings for these two?

Louis:

Ok, lets try something else.

In admin, under "My Store" there are two settings namely "Basis of Product Tax" and "Basis of Shipping Tax". What are your settings for these two?

Basis of Product Tax = Shipping
Basis of Shipping Tax = Store

Will that setting have an effect?

If tax-basis is set to "store", then you are charging tax based on the zone your store is located in ... basically the same as if your customer walked into your store to make the purchase.

If it's set to "shipping address" then if their shipping address matches a zone configured for taxes, then those taxes will be charged.