The interest rate, also known as the finance charge, is the amount you will be charged for borrowing the loan from SoFi, which accrues on a daily basis and includes no additional costs or fees.
The APR is a percentage that includes broader information such as any additional costs of the loan and can be affected based on when the loan is funded and the repayment schedule.
SoFi does not charge any fees, so typically the APR will equal the interest rate. In some cases, the APR will differ due to when the funds are disbursed, and when your first payment becomes due.