The answer is that some states do indeed want sales tax from this kind of sale, which they consider a sale of prewritten software.
The example I used is from a NY sales tax opinion regarding an Ohio corporation selling e-learning to NY customers. https://www.tax.ny.gov/pdf/advisory_opinions/sales/a09_2s.pdf is the link to their 2009 advisory opinion covering the subject.
Note that this opinion is different from their general rule, in which the e-learning was not sales taxable, due to the ongoing support and term of software use. NY claimed that was a sale of software. Perhaps your scenario does not meet that additional service and support standard.
Also, it should be noted that is on the end user.
Texas law governing e-services like yours is still evolving, but the safest position to take is to charge the tax, and remit it in Texas. That way you are covered in case an out of state user has a tax due, you collected in your home state.
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