If your California SOS number has seven digits, you can try leaving it bank in order to e-file your tax return.
You can click on the link to find your Secretary of State file number.CA Secretary of State. You can also check your Registration documents: The SOS file number is listed in your initial registration paperwork.
California Secretary of State File Numbers are assigned to all entities in the state of California by the Secretary of State. The business will either have a seven-digit corporation number or a 12 digit file number. You can call the office of the Secretary of State to see which one they have if they don't have their original application form.
Per the California Secretary of State Office, Corporations in CA have 7-digits numbers and LLCs have 12-digit numbers
For additional assistance on your filing number, please call the Secretary of State at (916) 653-6814.
Click here for "California Secretary of State File Number: How to Find, Use, and Manage It"