This is one of the most common issues I see with anyone who has horses. Make sure no matter what you ask of the horse you use the same cue for the same desired result. Changing cues or mixing them up to get a response is just creating confusion. Once I explain this it will seem simple but you have to be consistent in order to make a change.
While lunging I see 98% of horse owners clicking and kissing at their horse to get it to move around the pen. These same people also complain that their horses need spurs to move under saddle or the horse won’t pick up the trot or lope without extra coaxing.
These issues can all be avoided and fixed from the ground by simply dedicating one cue to one speed desired. For example I click three times to trot from a walk then kiss to canter or lope. this way the horse understands and there’s no miscommunication. Once the horse knows what to expect in the ground they will be more willing to try harder under saddle.
What you’ve created is a grey area and a lack of clear communication between you and your horse. If you click and kiss all the time together the horse doesn’t know weather you want to trot or canter when asked under saddle.
Another huge miscommunication I see that majority of horse owners do is click when asking to back the horse up either on the ground or under saddle. This click is another grey area. You use it to go forward yet use it when backing up. Change to the word “back” for back up and keep click for forward movement.
Keep your cues clear. If the horse is getting confused it’s most likely because you caused it. Step back and think how you can communicate more clearly and simply to your horse.