I got it working another way.
Added #include <hardware/uart.h> and #include <hardware/gpio.h> for low-level access
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Replaced
Serial1.setTX()/setRX()/begin()with:-
uart_init(uart1, BAUD) - Initialize UART1 at hardware level
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gpio_set_function(8, GPIO_FUNC_UART) - Configure GPIO 8 as UART TX
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gpio_set_function(9, GPIO_FUNC_UART) - Configure GPIO 9 as UART RX
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