why doesn't hardware work

Mmmmmmmm I'm gonna need some more information than that.

>> credit card processing hardware that attaches to an android cell phone.
What is the credit card processing hardware?  Make/model
What is the Android cell model?

>> why doesn't it work
Need to know if there is an error of some sorts.  Need more information to try and reproduce the issue you're experiencing.

I'm presuming the other person has the Android phone and the credit card application.

Possibly dirty card or worn magnetic stripe (on the card) would be my guess as to why it doesn't work.

In most situations, use of iPhone is a better choice in term of security and compliance with the credit card companies or banks.

If the merchant uses an Android phone for attaching to a credit card reader to process payment, I will not give my credit card for payment.

thanks.

I have not used hardware/software but seen others use hardware software. Upon thinking again, I realize that this answer gives me the most insight to a problem I have seen but not actually diagnosed.