The Bluetooth chip [ATBTLC1000A-MU-T](https://www.digikey.com/en/products/detail/microchip-technology/ATBTLC1000A-MU-T/6831868) is no longer available. Digikey suggest the [SX1231HIMLTRT](https://www.digikey.com/en/products/detail/semtech-corporation/SX1231HIMLTRT/4259558) as replacement part, but it's not pin-to-pin compatible. Microchip had a chip with same package [ISO1871](https://www.digikey.com/en/products/detail/microchip-technology/IS1871SF-102/13557888) but it's not pin-to-pin compatible. So, have you already choose a replacement part for this chip ?