You're using the wrong hotkey. When tuned to Tower hotkey 0 is initial checking, ready to taxi. To checking ready for takeoff it's hotkey 6.
You can find the following document in your PFE/Help folder...
ProFlight Commands used in PFE
PFE Default settings require you to use the Ctrl+Shift+ key combination together with one of the keys listed below EXCEPT for keys 0 thru 9 the ROGER key and the 'H' and 'L' keys, which only require a single keypress. Eg. For Virtual Co-Pilot mode use Ctrl+Shift+V but for Initial Check In you only need to use the zero key and to Roger ATC you use the '\' key
Facility Key Pilot Command/Message Game Commander
- ALL - E Declare an Emergency "Mayday, Mayday, Mayday"
- ALL - = Say Again/Repeat "Say Again"
- ALL - \ Roger/Readback "Roger"
- ALL -
D Toggle AI ground traffic detection on/off (default is ON) N/A
- ALL -
V Virtual Co-Pilot Mode - 4 Modes
OFF, COMM, COMM PLUS, P.I.C., P.I.C. PLUS N/A
- ALL - W Multi-functional. Skip to next taxi waypoint when TGS is active - Warp to selected waypoint during flight - Request another runway for takeoff/landing N/A
- ALL - H Plus one of the number keys (top row) 1 to 9 to request a higher altitude
- ALL - L Plus one of the number keys (top row) 1 to 9 to request a lower altitude
EMERG Y Positve answer (Yes) "Yes"
EMERG N Negative answer (No) "No"
Clearance 0 Initial Checkin, request CLEARANCE "Checking in"
Ground 0 Initial Checkin, ready to TAXI to RUNWAY "Checking in"
Ground 1 Deactivate/Reactivate toggle for TGS
Ground 5 Clear of the runway, request TAXI to TERMINAL "Request Taxi to Parking"
Ground 6 Request Radio Check "Request Radio Check"
Ground 7 Request Altimeter Setting "Request Altimeter Setting"
FSS 0 Request to Open Flight Plan "Open my Flight Plan"
FSS 1 Request to Close Flight Plan "Close my Flight Plan"
FSS 2 Extend ETA by 30 minutes "Extend my E.T.A."
FSS 3 Request Weather Advisories "Request Airport Advisories"
FSS 4 Request Center Frequency "Request Center Frequency"
FSS 6 Change Flight Plan to IFR/VFR (toggle) "Change my Flight Plan"
FSS 7 Request Airport Advisories "Request Airport Advisories"
FSS 8 Amend Flight Plan to land at next available airport "Amend my Flight Plan"
FSS 9 Report Position "Report Position"
Multicom 0 Initial Checkin (in the air only) "Checking in"
Multicom 2 Announce entering DOWNWIND "Entering Downwind"
Multicom 3 Announce turning BASE "Turning Base"
Multicom 4 Announce turning FINAL "Turning Final"
Multicom 5 Announce CLEAR of the RUNWAY "Request Taxi to Parking"
Multicom 6 Announce TAKING the RUNWAY "Taking the Runway"
Multicom 8 Announce DEPARTING the AREA "Departing the Area"
Unicom 0 Initial Checkin (in the air only) "Checking in"
Unicom 2 Announce entering DOWNWIND "Entering Downwind"
Unicom 3 Announce turning BASE "Turning Base"
Unicom 4 Announce turning FINAL "Turning Final"
Unicom 5 Announce CLEAR of the RUNWAY "Request Taxi to Parking"
Unicom 6 Announce TAKING the RUNWAY "Taking the Runway"
Unicom 7 Request Field Advisories "Request Field Advisories"
Unicom 8 Announce DEPARTING the AREA "Departing the Area"
Tower 0 Initial Checkin, ready to TAXI to RUNWAY "Checking in"
Tower 1 Initial Checkin for LANDING "Request Landing Clearance"
Tower 2 Report entering DOWNWIND "Entering Downwind"
Tower 3 Report turning BASE "Turning Base"
Tower 4 Report turning FINAL "Turning Final"
Tower 5 Request the Option (Touch 'n Go) "Request the Option"
Tower 6 Initial Checkin, ready for TAKEOFF "Request Takeoff Clearance"
Tower 7 Request Field Advisories "Request Field Advisories"
Tower 8 Report going to ALTERNATE Airport "Going to Alternate"
Tower 9 Report Go-Around/Missed-Approach "Declaring Missed Approach"
Tower w Request other Runway "Request other Runway"
Tower n Show another Runway "Show another Runway"
Tower y Accept that Runway "Accept that Runway"
Departure 0 Initial Checkin (if VFR, request Flight Following) "Checking in"
Departure 1 Request Cleared To Final At Pilot's Discretion "Request Cleared to Final"
Departure 3 Request LOWER ALTITUDE due to CLOUDS "Request Lower Altitude"
Departure 4 Request HIGHER ALTITUDE due to CLOUDS "Request Higher Altitude"
Departure 5 Request LOWER ALTITUDE due to TURBULENCE "Request Lower Altitude"
Departure 6 Request HIGHER ALTITUDE due to TURBULENCE "Request Higher Altitude"
Departure 7 Request VECTORS "Request Vectors"
Departure 8 Report AIRPORT IN SIGHT if VFR/VFR Approach "Airport in Sight"
Departure 9 Report POSITION "Report Position"
Center 0 Initial Checkin (if VFR, request Flight Following) "Checking in"
Center 1 Request Cleared To Final At Pilot's Discretion "Request Cleared to Final"
Center 3 Request LOWER ALTITUDE due to CLOUDS "Request Lower Altitude"
Center 4 Request HIGHER ALTITUDE due to CLOUDS "Request Higher Altitude"
Center 5 Request LOWER ALTITUDE due to TURBULENCE "Request Lower Altitude"
Center 6 Request HIGHER ALTITUDE due to TURBULENCE "Request Higher Altitude"
Center 7 Request VECTORS "Request Vectors"
Center 8 Report AIRPORT IN SIGHT if VFR/VFR Approach "Airport in Sight"
Center 9 Report POSITION "Report Position"
Approach 0 Initial Checkin (if VFR, request Flight Following) "Checking in"
Approach 1 Request Cleared To Final At Pilot's Discretion "Request Cleared to Final"
Approach 3 Request LOWER ALTITUDE due to CLOUDS "Request Lower Altitude"
Approach 4 Request HIGHER ALTITUDE due to CLOUDS "Request Higher Altitude"
Approach 5 Request LOWER ALTITUDE due to TURBULENCE "Request Lower Altitude"
Approach 6 Request HIGHER ALTITUDE due to TURBULENCE "Request Higher Altitude"
Approach 7 Request VECTORS "Request Vectors"
Approach 8 Report AIRPORT IN SIGHT if VFR/VFR Approach "Airport in Sight"
Approach 9 Report POSITION "Report Position"