Hi,
I think you may be confusing 2 separate things. Conditional Residents are required to submit the Biometrics Fee while filing the I-751 to remove conditions. You're a conditional resident until your ROC is approved and you're issued the 10 yr greencard. Read page 2 under Biometrics Fee (https://www.uscis.gov/sites/default/files/files/form/i-751instr.pdf). US Citizens and US lawful permanent residents do not need to file I-751 hence no biometrics fee is needed until USCIS sees a need for it. If one does not submit the exact required fee, the ROC package will be returned back to you causing further delays.
"1. Conditional Resident. Each conditional resident and conditional resident dependent included in the principal petitioner’s Form I-751 is required to submit a biometric services fee with this petition, in addition to the required filing fee...."
All the best!
SarahMay reacted to ala_tika in No biometrics fee needed for USC when I-751