You need to use the SS number on the schedule C of a single member LLC, this is from IRS: For federal income tax purposes, a single-member LLC classified as a disregarded entity generally must use the owner's social security number (SSN).

Here is link for you to read all the instruction for a single member LLC:

https://www.irs.gov/businesses/small-businesses-self-employed/single-member-limited-liability-compan...