I am trying to change the mode of my iris drone in gazebo using ROS Service from its base mode MANUAL to custom mode OFFBOARD. But when I hit the following command in the terminal, I get the following error. What should I do to resolve this issue

$ rosservice call /mavros/set_mode manual offboard

ERROR: Unable to send request. One of the fields has an incorrect type:
field base_mode must be unsigned integer type

srv file: uint8 MAVMODEPREFLIGHT=0 uint8 MAVMODESTABILIZEDISARMED=80 uint8 MAVMODESTABILIZEARMED=208 uint8 MAVMODEMANUALDISARMED=64 uint8 MAVMODEMANUALARMED=192 uint8 MAVMODEGUIDEDDISARMED=88 uint8 MAVMODEGUIDEDARMED=216 uint8 MAVMODEAUTODISARMED=92 uint8 MAVMODEAUTOARMED=220 uint8 MAVMODETESTDISARMED=66 uint8 MAVMODETESTARMED=194 uint8 basemode string custommode --- bool mode_sent