There were two Parliaments summoned in 1399. As the first, called to Westminster in Richard II's name, met on 30 Sept., the day after the King abdicated, it was regarded as a gathering of 'estates and people' and used as the instrument of deposition. The other, summoned by Henry IV, met six days later, but with identical membership.
Met at Westminster. See Appendix C4 of the Introductory Survey for the composition of this Parliament, and see The Parliament Rolls of Medieval England (External subscription site) for further information.