Ring doorbell pro & mechanical doorbell issue - "ding" instead of "ding-dong"

Hello, I recently installed my Ring Doorbell Pro and hardwired it to my mechanical doorbell. After installation, when I press the doorbell, it only rings one of the two bells (i.e., just "ding" instead of "ding-dong"). There's one unique thing about my internal doorbell. It has three wires connecting to terminals that are labeled "1", "2", and "com". I installed the Pro Power Kit V2 by connecting one wire to the "1" terminal and another to the "com" terminal. I have a feeling it has something to do with how the Pro Power Kit V2 was installed, because this same thing (i.e., "ding" not "ding-dong") happens now when I press the other original doorbell on my house (i.e., not the newly installed Ring Doorbell Pro). Any help is appreciated!