I have been looking through the Oklahoma instructions, and don't see a required attachment for the Credit for Contributions to a Scholarship-Granting Organization.
In the Oklahoma return, form 511-CR is added to list the credit, but I don't see a requirement to add anything else. Can you point me to some instructions that say otherwise?
The instructions to Form 511-CR for line 20 state in the last sentence of the first paragraph "If claiming the 75% credit, evidence of the written commitment must be provided. 68 OS Sec.2357.206 and Rule 710:50-15-114. Go to osfkids.org and under FAQ "what form do I submit to claim my tax credits?", there is a link to the form and the instructions.
TurboTax does not have a way to add random forms to the tax return. This is because the tax return is in an XML format, and does not include PDF documents unless both TurboTax and the state plan for it.
No matter, it is not unusual to have this situation of needing to send additional documentation to the state.
I talked to the Oklahoma Tax Commission, and they said just send them a letter with your name and Social Security number at the top. If you print all your forms (highly recommended that you at least keep a PDF copy of your return) and you have a 511-EF, then attach a copy of it to your letter (this is the document that shows that you e-filed your state return).
If not, just make it clear what you are doing ("The taxpayer shall provide evidence of the written commitment to the Tax Commission when the tax return claiming the credit is filed the first year."), and that you have e-filed your Oklahoma return under the name and SS number above.
The Tax Commission will figure it out.