review the entries you made. it is likely, the $600 got entered twice.
you can use
1099-NEC or
1099-MISC - linked to schedule C por
or enter on the line for 1099 not received
but use only one.
using 1099-NEC or 1099-MISC is not required. they're really for your records only. the amounts on them get transferred to the applicable form but none of the details are sent o the IRS
