The number of contractors that can be added to a TPAR form is 50.
The limitation is due to the ATO specifications. For more information on how to lodge more than 50, see below ATO link:
https://www.ato.gov.au/business/reports-and-returns/taxable-payments-annual-report/lodge-your-tpar/#Taxprofessionals
Please note: Prior to 2020 the limit is 30.