Why am I not able to pair both hearing aids with the myPhonak app?

Why do I have to pair my hearing aids one by one? During the initial pairing I can select only the right or the left one, never both hearing aids together at the same time.

The hearing aids were not fitted as a pair. Please contact your hearing care professional to have the hearing aids fitted again (with the latest available fitting software). Hearing aids must be fitted together to connect with the myPhonak app at the same time.

Not all pairs of hearing aids are compatible with the app. Pairs of hearing aids with Bluetooth functionality, where both devices are of the same type (matching model and performance level), are compatible with myPhonak. Additionally, certain mixed combinations of hearing aid types are also supported. Further details can be found here:
Connecting the myPhonak app to hearing aids with different types of devices -> Hearing aid combinations supported with myPhonak app