Payroll on 24 month STEM OPT period

Hi very urgent, please

I applied for OPT Extension while working through employer A, for client B, during my application under process changed to new employer, new employer offer letter says we will provide extensive training initially and then place at client location and salary $$ per year, I sent my offer letter and e-verification number as an amendment to my application, I got my extension, but my question is my new employer didn’t paid anything as I’m initially in training and recently placed at client location, so is it mandatory that payroll need to be run even I’m in training with new employer while on my STEM OPT Extension period

at this point if i get another position, is there any impact in future (applying for h1b, traveling etc) due to that unpaid duration or will it be considered as unemployment and counted towards the 60 days unemployment grace period on STEM OPT, please advice. thanks