Forecaster predict - No 'freq' argument was found

Question

I'm tring to run forecaster.predict but keeps giving a 'no freq' error:

The freq attribute of the time index is required, but found: None. Please specify the freq argument when setting the time index.

I've split my dataset in training and test. My dataset is constant with daily values, and even if I use asfreq('D') to set the fh index to daily, it does not work. I'm setting the fh using the train index.

Can anybody help me, please? Thanks!

Code: https://github.com/dhgrassi/Grupo-de-Estudos-DS/blob/main/TCC_Teste_com_Dados_Reais.ipynb