Technically, basis in nondeductible traditional IRA contributions is not permitted to be rolled over to a 403(b), so it would seem that the $1,500 should be removed from the 403(b) as an excess contribution along with the attributable net income. The $1,500 (not the attributable net income) could then potentially be deposited into a Roth IRA as a late conversion (a late rollover because a Roth conversion is a particular type of rollover) under IRS Rev. Proc. 2020-46 due to financial institution error.
