I purchased a BetaFPV F3 DSM https://micro-motor-warehouse.com/collections/flight-controllers-1/products/betafpv-fc-f3 from Micro Motor Warehouse recently. I bound it to my Spektrum DX7 Tx in DSM2 mode as Benedikt suggested. Then I connected the FC to BetaFlight, installed the proper F3 firmware and adjusted all of the stick travels to within the proper limits. I assigned stick A on my DX7 for arming on AUX1 and switch B to change flight modes on AUX2 adjusting the travels for each to the proper ranges in BetaFlight. All of the stick movements show to be within the proper ranges and switch B for changing works and will change from Angle to Horizon to Heads Free without any problem, however switch A will not Arm the FC.
Any suggestions would be greatly appreciated.