Travelling with pet

I will be travelling in Perú with my Yorkie. She is old, very quiet, friendly with everybody, and used to travel with me everywhere, in a frontpack (something fit for international flights).
I will use public transport, specially buses.
I want to know if there is any problem to get into intercity and/or international buses with a smal dog in a soft container. Is it usefull to have a therapeutic pet certificate?
Thanks for any advice.

I also have my cat and I am also used to traveling with her in my local areas if  you are traveling in your local areas i think no issue to travel with pets yes but if traveling in international status definitely you must think before travel with pets

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