spf.schwab.com has no NS records.
NS records for this zone are defined at schwab.com.
NS records for this zone are defined at schwab.com.
Question and response
Question
dig spf.schwab.com. NS
Answer
The response has no answer records.
Authority
schwab.com. 600 SOA d33pf2cdc.schwab.com. dnsadmin.schwab.com. 2023022033 3600 900 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0