The 2021 CA Schedule S instructions, Section D :
2021 Instructions for Schedule S | FTB.ca.gov
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They still list AZ, GU, OR, & VA as the states where the CA non-residents can still claim this credit.
1) Check your tax forms to make sure that the proper amount carried from the AZ tax return to the CA nonresident return. (I suspect you have to prepare your Resident AZ tax return first....which is backwards from most other Resident/non-resident state situations)
2) You'll probably have to call the CA FTB, (at whatever phone number their notice provided), to see what evidence they require, or if there is some particular reason that they disallowed it (so far?). Perhaps they think you were declaring more CA-income as being taxed than was the actual situation, or perhaps they want to see a printed copy of your AZ tax return, or CA-sourced income documents to prove your claim. You'll really have to ask the FTB.
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@VolvoGirl You do CA taxes....any added input?