Welcome to TRF.
There are two issues to address.
1.) You have to make sure you are installing the igniters correctly. If you do not place the igniter in contact with the propellant grain inside the motor, or you short the leads, or break the bridgewire, the motor will fail to ignite.
2.) An igniter is a resistor and the electrical heating of the igniter is due to current not voltage. The minimum all-fire current for Estes igniters is 2 amps and the resistance of the typical bridgewire is 0.1 ohms. The minimum power in watts is equal to the resistance multiplied by the minimum current squared or P = R x I^2 = 0.8 ohms x 2 volts^2 = 3.2 watts and the minimum voltage require is the resistance times the current or V = R x I = 0.8 ohms x 2 amps = 1.6 volts.
The launcher wire and battery resistance require you to use a battery voltage higher than 1.6 volts, and if you want prompt ignition you want to use more than the minimum all-fire current. A factor of 2 higher current is a good goal. If that is the option chosen, you use ohms law, V = RI to determine the minimum battery voltage and current required. If you want to deliver 4 amps to the igniter, the voltage must be greater than 3.2 volts plus enough extra to overcome the resistance of the wiring, and the battery must be able to actually deliver amps of current.
A new alkaline 9 volt battery can supply between 3 to 5 amps. This means the internal resistance of the battery R = V/R = 9/5 = 1.8 ohms to 9/3 = 3 ohms. If we assume the resistance of the launcher is 0.2 ohms, the total resistance of your launching circuit is R = 0.8 ohms (igniter) + 0.2 ohms (launcher) + 1.8 to 3 ohms (battery) = 2.8 to 4 ohms total. The current pushed through the igniter is simple I = V / R = 9/4 = 2.25 amps to 9/2.8 = 3.2 amps. If you have dirty clips the resistance goes up and the current delivered goes down. Please note that even though you have plenty of voltage, the total circuit resistant reduces the current dramatically, and in the case of a 3 amp, 9 volt battery any dirt will prevent the igniter from firing. If you we using a regular (non-alkaline) 9 volt battery, the internal resistance of the battery is probably greater than 5 ohms and you will not get the minimum 2 amps through the launcher to activate the igniter.
I know it may be confusing, even to the experienced person, but you have to be sure your battery, regardless of the voltage rating, is up to the job, supplying enough current, to activate the igniter.
Bob