Wow, you could try doing some research on your own like a basic search. https://www.law.cornell.edu/cfr/text/26/301.6221(b)-1
https://www.thetaxadviser.com/issues/2018/jul/irs-final-regs-electing-out-centralized-partner[produc...
https://www.thetaxadviser.com/issues/2021/feb/centralized-partner[product key removed]e-related-item...
