H1B Transfer Question -II

I am currently with Employer A with H1B 2022 and I have another H1B with employer B which is valid till 2023( The H1B isn’t E-Verified as the both employer A and Employer B are sisters company) , however now Employer A “s end client wants me as FTE , now which H1B document Should I produce to the client immgiration law , as of now I have employer A H1B active with pay stubs till today(he didn’t cancel it) So please guide me how should I move to end client process

If employer A is paying you, it would mean that your H1B from employer A is active and you should provide the I-797 approval notice copy of H1B from employer A to the immigration lawyer of your client.